Merge branch 'stb-image-fuzzing-fixes' of https://github.com/rcgordon/stb into working

stb_image.h

@@ -93,22 +93,30 @@ RECENT REVISION HISTORY:
     Carmelo J Fdez-Aguera
 
  Bug & warning fixes
-    Marc LeBlanc            David Woo          Guillaume George   Martins Mozeiko
-    Christpher Lloyd        Jerry Jansson      Joseph Thomson     Phil Jordan
-    Dave Moore              Roy Eltham         Hayaki Saito       Nathan Reed
-    Won Chun                Luke Graham        Johan Duparc       Nick Verigakis
-    the Horde3D community   Thomas Ruf         Ronny Chevalier    github:rlyeh
-    Janez Zemva             John Bartholomew   Michal Cichon      github:romigrou
-    Jonathan Blow           Ken Hamada         Tero Hanninen      github:svdijk
-    Laurent Gomila          Cort Stratton      Sergio Gonzalez    github:snagar
-    Aruelien Pocheville     Thibault Reuille   Cass Everitt       github:Zelex
-    Ryamond Barbiero        Paul Du Bois       Engin Manap        github:grim210
-    Aldo Culquicondor       Philipp Wiesemann  Dale Weiler        github:sammyhw
-    Oriol Ferrer Mesia      Josh Tobin         Matthew Gregan     github:phprus
-    Julian Raschke          Gregory Mullen     Baldur Karlsson    github:poppolopoppo
-    Christian Floisand      Kevin Schmidt      JR Smith           github:darealshinji
-    Brad Weinberger         Matvey Cherevko    Luca Sas           github:Michaelangel007
-    Blazej Dariusz Roszkowski                  Alexander Veselov  Zack Middleton
+    Marc LeBlanc            David Woo          Guillaume George     Martins Mozeiko
+    Christpher Lloyd        Jerry Jansson      Joseph Thomson       Blazej Dariusz Roszkowski
+    Phil Jordan                                Dave Moore           Roy Eltham         
+    Hayaki Saito            Nathan Reed        Won Chun
+    Luke Graham             Johan Duparc       Nick Verigakis       the Horde3D community   
+    Thomas Ruf              Ronny Chevalier                         github:rlyeh           
+    Janez Zemva             John Bartholomew   Michal Cichon        github:romigrou        
+    Jonathan Blow           Ken Hamada         Tero Hanninen        github:svdijk          
+                            Laurent Gomila     Cort Stratton        github:snagar          
+    Aruelien Pocheville     Sergio Gonzalez    Thibault Reuille     github:Zelex           
+    Cass Everitt            Ryamond Barbiero                        github:grim210         
+    Paul Du Bois            Engin Manap        Aldo Culquicondor    github:sammyhw         
+    Philipp Wiesemann       Dale Weiler        Oriol Ferrer Mesia   github:phprus             
+    Josh Tobin                                 Matthew Gregan       github:poppolopoppo    
+    Julian Raschke          Gregory Mullen     Christian Floisand   github:darealshinji    
+    Baldur Karlsson         Kevin Schmidt      JR Smith             github:Michaelangel007 
+                            Brad Weinberger    Matvey Cherevko      [reserved]
+    Luca Sas                Alexander Veselov  Zack Middleton       [reserved]
+    Ryan C. Gordon          [reserved]                              [reserved]
+                     DO NOT ADD YOUR NAME HERE      
+
+  To add your name to the credits, pick a random blank space in the middle and fill it.
+  80% of merge conflicts on stb PRs are due to people adding their name at the end
+  of the credits.
 */
 
 #ifndef STBI_INCLUDE_STB_IMAGE_H
@@ -318,7 +326,14 @@ RECENT REVISION HISTORY:
 //   - If you use STBI_NO_PNG (or _ONLY_ without PNG), and you still
 //     want the zlib decoder to be available, #define STBI_SUPPORT_ZLIB
 //
-
+//  - If you define STBI_MAX_DIMENSIONS, stb_image will reject images greater
+//    than that size (in either width or height) without further processing.
+//    This is to let programs in the wild set an upper bound to prevent
+//    denial-of-service attacks on untrusted data, as one could generate a
+//    valid image of gigantic dimensions and force stb_image to allocate a
+//    huge block of memory and spend disproportionate time decoding it. By
+//    default this is set to (1 << 24), which is 16777216, but that's still
+//    very big.
 
 #ifndef STBI_NO_STDIO
 #include <stdio.h>
@@ -734,6 +749,10 @@ static int stbi__sse2_available(void)
 #define STBI_SIMD_ALIGN(type, name) type name
 #endif
 
+#ifndef STBI_MAX_DIMENSIONS
+#define STBI_MAX_DIMENSIONS (1 << 24)
+#endif
+
 ///////////////////////////////////////////////
 //
 //  stbi__context struct and start_xxx functions
@@ -792,12 +811,17 @@ static int stbi__stdio_read(void *user, char *data, int size)
 
 static void stbi__stdio_skip(void *user, int n)
 {
+   int ch;
    fseek((FILE*) user, n, SEEK_CUR);
+   ch = fgetc((FILE*) user);  /* have to read a byte to reset feof()'s flag */
+   if (ch != EOF) {
+      ungetc(ch, (FILE *) user);  /* push byte back onto stream if valid. */
+   }
 }
 
 static int stbi__stdio_eof(void *user)
 {
-   return feof((FILE*) user);
+   return feof((FILE*) user) || ferror((FILE *) user);
 }
 
 static stbi_io_callbacks stbi__stdio_callbacks =
@@ -1174,8 +1198,10 @@ static unsigned char *stbi__load_and_postprocess_8bit(stbi__context *s, int *x,
    if (result == NULL)
       return NULL;
 
+   // it is the responsibility of the loaders to make sure we get either 8 or 16 bit.
+   STBI_ASSERT(ri.bits_per_channel == 8 || ri.bits_per_channel == 16);
+
    if (ri.bits_per_channel != 8) {
-      STBI_ASSERT(ri.bits_per_channel == 16);
       result = stbi__convert_16_to_8((stbi__uint16 *) result, *x, *y, req_comp == 0 ? *comp : req_comp);
       ri.bits_per_channel = 8;
    }
@@ -1198,8 +1224,10 @@ static stbi__uint16 *stbi__load_and_postprocess_16bit(stbi__context *s, int *x,
    if (result == NULL)
       return NULL;
 
+   // it is the responsibility of the loaders to make sure we get either 8 or 16 bit.
+   STBI_ASSERT(ri.bits_per_channel == 8 || ri.bits_per_channel == 16);
+
    if (ri.bits_per_channel != 16) {
-      STBI_ASSERT(ri.bits_per_channel == 8);
       result = stbi__convert_8_to_16((stbi_uc *) result, *x, *y, req_comp == 0 ? *comp : req_comp);
       ri.bits_per_channel = 16;
    }
@@ -1548,6 +1576,7 @@ stbi_inline static int stbi__at_eof(stbi__context *s)
 #else
 static void stbi__skip(stbi__context *s, int n)
 {
+   if (n == 0) return;  // already there!
    if (n < 0) {
       s->img_buffer = s->img_buffer_end;
       return;
@@ -1690,7 +1719,7 @@ static unsigned char *stbi__convert_format(unsigned char *data, int img_n, int r
          STBI__CASE(4,1) { dest[0]=stbi__compute_y(src[0],src[1],src[2]);                   } break;
          STBI__CASE(4,2) { dest[0]=stbi__compute_y(src[0],src[1],src[2]); dest[1] = src[3]; } break;
          STBI__CASE(4,3) { dest[0]=src[0];dest[1]=src[1];dest[2]=src[2];                    } break;
-         default: STBI_ASSERT(0);
+         default: STBI_ASSERT(0); STBI_FREE(data); STBI_FREE(good); return stbi__errpuc("unsupported", "Unsupported format conversion");
       }
       #undef STBI__CASE
    }
@@ -1747,7 +1776,7 @@ static stbi__uint16 *stbi__convert_format16(stbi__uint16 *data, int img_n, int r
          STBI__CASE(4,1) { dest[0]=stbi__compute_y_16(src[0],src[1],src[2]);                   } break;
          STBI__CASE(4,2) { dest[0]=stbi__compute_y_16(src[0],src[1],src[2]); dest[1] = src[3]; } break;
          STBI__CASE(4,3) { dest[0]=src[0];dest[1]=src[1];dest[2]=src[2];                       } break;
-         default: STBI_ASSERT(0);
+         default: STBI_ASSERT(0); STBI_FREE(data); STBI_FREE(good); return (stbi__uint16*) stbi__errpuc("unsupported", "Unsupported format conversion");
       }
       #undef STBI__CASE
    }
@@ -2056,7 +2085,7 @@ stbi_inline static int stbi__extend_receive(stbi__jpeg *j, int n)
 
    sgn = (stbi__int32)j->code_buffer >> 31; // sign bit is always in MSB
    k = stbi_lrot(j->code_buffer, n);
-   STBI_ASSERT(n >= 0 && n < (int) (sizeof(stbi__bmask)/sizeof(*stbi__bmask)));
+   if (n < 0 || n >= (int) (sizeof(stbi__bmask)/sizeof(*stbi__bmask))) return 0;
    j->code_buffer = k & ~stbi__bmask[n];
    k &= stbi__bmask[n];
    j->code_bits -= n;
@@ -2167,6 +2196,7 @@ static int stbi__jpeg_decode_block_prog_dc(stbi__jpeg *j, short data[64], stbi__
       // first scan for DC coefficient, must be first
       memset(data,0,64*sizeof(data[0])); // 0 all the ac values now
       t = stbi__jpeg_huff_decode(j, hdc);
+      if (t == -1) return stbi__err("can't merge dc and ac", "Corrupt JPEG");
       diff = t ? stbi__extend_receive(j, t) : 0;
 
       dc = j->img_comp[b].dc_pred + diff;
@@ -3157,6 +3187,8 @@ static int stbi__process_frame_header(stbi__jpeg *z, int scan)
    p  = stbi__get8(s);            if (p != 8) return stbi__err("only 8-bit","JPEG format not supported: 8-bit only"); // JPEG baseline
    s->img_y = stbi__get16be(s);   if (s->img_y == 0) return stbi__err("no header height", "JPEG format not supported: delayed height"); // Legal, but we don't handle it--but neither does IJG
    s->img_x = stbi__get16be(s);   if (s->img_x == 0) return stbi__err("0 width","Corrupt JPEG"); // JPEG requires
+   if (s->img_y > STBI_MAX_DIMENSIONS) return stbi__err("too large","Very large image (corrupt?)");
+   if (s->img_x > STBI_MAX_DIMENSIONS) return stbi__err("too large","Very large image (corrupt?)");
    c = stbi__get8(s);
    if (c != 3 && c != 1 && c != 4) return stbi__err("bad component count","Corrupt JPEG");
    s->img_n = c;
@@ -4037,16 +4069,23 @@ typedef struct
    stbi__zhuffman z_length, z_distance;
 } stbi__zbuf;
 
+stbi_inline static int stbi__zeof(stbi__zbuf *z)
+{
+   return (z->zbuffer >= z->zbuffer_end);
+}
+
 stbi_inline static stbi_uc stbi__zget8(stbi__zbuf *z)
 {
-   if (z->zbuffer >= z->zbuffer_end) return 0;
-   return *z->zbuffer++;
+   return stbi__zeof(z) ? 0 : *z->zbuffer++;
 }
 
 static void stbi__fill_bits(stbi__zbuf *z)
 {
    do {
-      STBI_ASSERT(z->code_buffer < (1U << z->num_bits));
+      if (z->code_buffer >= (1U << z->num_bits)) {
+        z->zbuffer = z->zbuffer_end;  /* treat this as EOF so we fail. */
+        return;
+      }
       z->code_buffer |= (unsigned int) stbi__zget8(z) << z->num_bits;
       z->num_bits += 8;
    } while (z->num_bits <= 24);
@@ -4071,10 +4110,11 @@ static int stbi__zhuffman_decode_slowpath(stbi__zbuf *a, stbi__zhuffman *z)
    for (s=STBI__ZFAST_BITS+1; ; ++s)
       if (k < z->maxcode[s])
          break;
-   if (s == 16) return -1; // invalid code!
+   if (s >= 16) return -1; // invalid code!
    // code size is s, so:
    b = (k >> (16-s)) - z->firstcode[s] + z->firstsymbol[s];
-   STBI_ASSERT(z->size[b] == s);
+   if (b >= sizeof (z->size)) return -1; // some data was corrupt somewhere!
+   if (z->size[b] != s) return -1;  // was originally an assert, but report failure instead.
    a->code_buffer >>= s;
    a->num_bits -= s;
    return z->value[b];
@@ -4083,7 +4123,12 @@ static int stbi__zhuffman_decode_slowpath(stbi__zbuf *a, stbi__zhuffman *z)
 stbi_inline static int stbi__zhuffman_decode(stbi__zbuf *a, stbi__zhuffman *z)
 {
    int b,s;
-   if (a->num_bits < 16) stbi__fill_bits(a);
+   if (a->num_bits < 16) {
+      if (stbi__zeof(a)) {
+         return -1;   /* report error for unexpected end of data. */
+      }
+      stbi__fill_bits(a);
+   }
    b = z->fast[a->code_buffer & STBI__ZFAST_MASK];
    if (b) {
       s = b >> 9;
@@ -4097,13 +4142,16 @@ stbi_inline static int stbi__zhuffman_decode(stbi__zbuf *a, stbi__zhuffman *z)
 static int stbi__zexpand(stbi__zbuf *z, char *zout, int n)  // need to make room for n bytes
 {
    char *q;
-   int cur, limit, old_limit;
+   unsigned int cur, limit, old_limit;
    z->zout = zout;
    if (!z->z_expandable) return stbi__err("output buffer limit","Corrupt PNG");
-   cur   = (int) (z->zout     - z->zout_start);
-   limit = old_limit = (int) (z->zout_end - z->zout_start);
-   while (cur + n > limit)
+   cur   = (unsigned int) (z->zout - z->zout_start);
+   limit = old_limit = (unsigned) (z->zout_end - z->zout_start);
+   if (UINT_MAX - cur < (unsigned) n) return stbi__err("outofmem", "Out of memory");
+   while (cur + n > limit) {
+      if(limit > UINT_MAX / 2) return stbi__err("outofmem", "Out of memory");
       limit *= 2;
+   }
    q = (char *) STBI_REALLOC_SIZED(z->zout_start, old_limit, limit);
    STBI_NOTUSED(old_limit);
    if (q == NULL) return stbi__err("outofmem", "Out of memory");
@@ -4201,11 +4249,12 @@ static int stbi__compute_huffman_codes(stbi__zbuf *a)
             c = stbi__zreceive(a,2)+3;
             if (n == 0) return stbi__err("bad codelengths", "Corrupt PNG");
             fill = lencodes[n-1];
-         } else if (c == 17)
+         } else if (c == 17) {
             c = stbi__zreceive(a,3)+3;
-         else {
-            STBI_ASSERT(c == 18);
+         } else if (c == 18) {
             c = stbi__zreceive(a,7)+11;
+         } else {
+            return stbi__err("bad codelengths", "Corrupt PNG");
          }
          if (ntot - n < c) return stbi__err("bad codelengths", "Corrupt PNG");
          memset(lencodes+n, fill, c);
@@ -4231,7 +4280,7 @@ static int stbi__parse_uncompressed_block(stbi__zbuf *a)
       a->code_buffer >>= 8;
       a->num_bits -= 8;
    }
-   STBI_ASSERT(a->num_bits == 0);
+   if (a->num_bits < 0) return stbi__err("zlib corrupt","Corrupt PNG");
    // now fill header the normal way
    while (k < 4)
       header[k++] = stbi__zget8(a);
@@ -4253,6 +4302,7 @@ static int stbi__parse_zlib_header(stbi__zbuf *a)
    int cm    = cmf & 15;
    /* int cinfo = cmf >> 4; */
    int flg   = stbi__zget8(a);
+   if (stbi__zeof(a)) return stbi__err("bad zlib header","Corrupt PNG"); // zlib spec
    if ((cmf*256+flg) % 31 != 0) return stbi__err("bad zlib header","Corrupt PNG"); // zlib spec
    if (flg & 32) return stbi__err("no preset dict","Corrupt PNG"); // preset dictionary not allowed in png
    if (cm != 8) return stbi__err("bad compression","Corrupt PNG"); // DEFLATE required for png
@@ -4514,7 +4564,7 @@ static int stbi__create_png_image_raw(stbi__png *a, stbi_uc *raw, stbi__uint32 r
          return stbi__err("invalid filter","Corrupt PNG");
 
       if (depth < 8) {
-         STBI_ASSERT(img_width_bytes <= x);
+         if (img_width_bytes > x) return stbi__err("invalid width","Corrupt PNG");
          cur += x*out_n - img_width_bytes; // store output to the rightmost img_len bytes, so we can decode in place
          filter_bytes = 1;
          width = img_width_bytes;
@@ -4909,8 +4959,10 @@ static int stbi__parse_png_file(stbi__png *z, int scan, int req_comp)
             if (!first) return stbi__err("multiple IHDR","Corrupt PNG");
             first = 0;
             if (c.length != 13) return stbi__err("bad IHDR len","Corrupt PNG");
-            s->img_x = stbi__get32be(s); if (s->img_x > (1 << 24)) return stbi__err("too large","Very large image (corrupt?)");
-            s->img_y = stbi__get32be(s); if (s->img_y > (1 << 24)) return stbi__err("too large","Very large image (corrupt?)");
+            s->img_x = stbi__get32be(s);
+            s->img_y = stbi__get32be(s);
+            if (s->img_y > STBI_MAX_DIMENSIONS) return stbi__err("too large","Very large image (corrupt?)");
+            if (s->img_x > STBI_MAX_DIMENSIONS) return stbi__err("too large","Very large image (corrupt?)");
             z->depth = stbi__get8(s);  if (z->depth != 1 && z->depth != 2 && z->depth != 4 && z->depth != 8 && z->depth != 16)  return stbi__err("1/2/4/8/16-bit only","PNG not supported: 1/2/4/8/16-bit only");
             color = stbi__get8(s);  if (color > 6)         return stbi__err("bad ctype","Corrupt PNG");
             if (color == 3 && z->depth == 16)                  return stbi__err("bad ctype","Corrupt PNG");
@@ -5059,10 +5111,12 @@ static void *stbi__do_png(stbi__png *p, int *x, int *y, int *n, int req_comp, st
    void *result=NULL;
    if (req_comp < 0 || req_comp > 4) return stbi__errpuc("bad req_comp", "Internal error");
    if (stbi__parse_png_file(p, STBI__SCAN_load, req_comp)) {
-      if (p->depth < 8)
+      if (p->depth <= 8)
          ri->bits_per_channel = 8;
+      else if (p->depth == 16)
+         ri->bits_per_channel = 16;
       else
-         ri->bits_per_channel = p->depth;
+         return stbi__errpuc("bad bits_per_channel", "PNG not supported: unsupported color depth");
       result = p->out;
       p->out = NULL;
       if (req_comp && req_comp != p->s->img_out_n) {
@@ -5223,6 +5277,8 @@ static void *stbi__bmp_parse_header(stbi__context *s, stbi__bmp_data *info)
    info->mr = info->mg = info->mb = info->ma = 0;
    info->extra_read = 14;
 
+   if (info->offset < 0) return stbi__errpuc("bad BMP", "bad BMP");
+
    if (hsz != 12 && hsz != 40 && hsz != 56 && hsz != 108 && hsz != 124) return stbi__errpuc("unknown BMP", "BMP type not supported: unknown");
    if (hsz == 12) {
       s->img_x = stbi__get16le(s);
@@ -5314,6 +5370,9 @@ static void *stbi__bmp_load(stbi__context *s, int *x, int *y, int *comp, int req
    flip_vertically = ((int) s->img_y) > 0;
    s->img_y = abs((int) s->img_y);
 
+   if (s->img_y > STBI_MAX_DIMENSIONS) return stbi__errpuc("too large","Very large image (corrupt?)");
+   if (s->img_x > STBI_MAX_DIMENSIONS) return stbi__errpuc("too large","Very large image (corrupt?)");
+
    mr = info.mr;
    mg = info.mg;
    mb = info.mb;
@@ -5329,6 +5388,9 @@ static void *stbi__bmp_load(stbi__context *s, int *x, int *y, int *comp, int req
    }
    if (psize == 0) {
       STBI_ASSERT(info.offset == s->callback_already_read + (int) (s->img_buffer - s->img_buffer_original));
+      if (info.offset != s->callback_already_read + (s->img_buffer - s->buffer_start)) {
+        return stbi__errpuc("bad offset", "Corrupt BMP");
+      }
    }
 
    if (info.bpp == 24 && ma == 0xff000000)
@@ -5423,6 +5485,7 @@ static void *stbi__bmp_load(stbi__context *s, int *x, int *y, int *comp, int req
          gshift = stbi__high_bit(mg)-7; gcount = stbi__bitcount(mg);
          bshift = stbi__high_bit(mb)-7; bcount = stbi__bitcount(mb);
          ashift = stbi__high_bit(ma)-7; acount = stbi__bitcount(ma);
+         if (rcount > 8 || gcount > 8 || bcount > 8 || acount > 8) { STBI_FREE(out); return stbi__errpuc("bad masks", "Corrupt BMP"); }
       }
       for (j=0; j < (int) s->img_y; ++j) {
          if (easy) {
@@ -5647,6 +5710,9 @@ static void *stbi__tga_load(stbi__context *s, int *x, int *y, int *comp, int req
    STBI_NOTUSED(tga_x_origin); // @TODO
    STBI_NOTUSED(tga_y_origin); // @TODO
 
+   if (tga_height > STBI_MAX_DIMENSIONS) return stbi__errpuc("too large","Very large image (corrupt?)");
+   if (tga_width > STBI_MAX_DIMENSIONS) return stbi__errpuc("too large","Very large image (corrupt?)");
+
    //   do a tiny bit of precessing
    if ( tga_image_type >= 8 )
    {
@@ -5686,6 +5752,11 @@ static void *stbi__tga_load(stbi__context *s, int *x, int *y, int *comp, int req
       //   do I need to load a palette?
       if ( tga_indexed)
       {
+         if (tga_palette_len == 0) {  /* you have to have at least one entry! */
+            STBI_FREE(tga_data);
+            return stbi__errpuc("bad palette", "Corrupt TGA");
+         }
+
          //   any data to skip? (offset usually = 0)
          stbi__skip(s, tga_palette_start );
          //   load the palette
@@ -5894,6 +5965,9 @@ static void *stbi__psd_load(stbi__context *s, int *x, int *y, int *comp, int req
    h = stbi__get32be(s);
    w = stbi__get32be(s);
 
+   if (h > STBI_MAX_DIMENSIONS) return stbi__errpuc("too large","Very large image (corrupt?)");
+   if (w > STBI_MAX_DIMENSIONS) return stbi__errpuc("too large","Very large image (corrupt?)");
+
    // Make sure the depth is 8 bits.
    bitdepth = stbi__get16be(s);
    if (bitdepth != 8 && bitdepth != 16)
@@ -6248,6 +6322,10 @@ static void *stbi__pic_load(stbi__context *s,int *px,int *py,int *comp,int req_c
 
    x = stbi__get16be(s);
    y = stbi__get16be(s);
+
+   if (y > STBI_MAX_DIMENSIONS) return stbi__errpuc("too large","Very large image (corrupt?)");
+   if (x > STBI_MAX_DIMENSIONS) return stbi__errpuc("too large","Very large image (corrupt?)");
+
    if (stbi__at_eof(s))  return stbi__errpuc("bad file","file too short (pic header)");
    if (!stbi__mad3sizes_valid(x, y, 4, 0)) return stbi__errpuc("too large", "PIC image too large to decode");
 
@@ -6356,6 +6434,9 @@ static int stbi__gif_header(stbi__context *s, stbi__gif *g, int *comp, int is_in
    g->ratio = stbi__get8(s);
    g->transparent = -1;
 
+   if (g->w > STBI_MAX_DIMENSIONS) return stbi__err("too large","Very large image (corrupt?)");
+   if (g->h > STBI_MAX_DIMENSIONS) return stbi__err("too large","Very large image (corrupt?)");
+
    if (comp != 0) *comp = 4;  // can't actually tell whether it's 3 or 4 until we parse the comments
 
    if (is_info) return 1;
@@ -6905,6 +6986,9 @@ static float *stbi__hdr_load(stbi__context *s, int *x, int *y, int *comp, int re
    token += 3;
    width = (int) strtol(token, NULL, 10);
 
+   if (height > STBI_MAX_DIMENSIONS) return stbi__errpf("too large","Very large image (corrupt?)");
+   if (width > STBI_MAX_DIMENSIONS) return stbi__errpf("too large","Very large image (corrupt?)");
+
    *x = width;
    *y = height;
 
@@ -7219,6 +7303,9 @@ static void *stbi__pnm_load(stbi__context *s, int *x, int *y, int *comp, int req
    if (!stbi__pnm_info(s, (int *)&s->img_x, (int *)&s->img_y, (int *)&s->img_n))
       return 0;
 
+   if (s->img_y > STBI_MAX_DIMENSIONS) return stbi__errpuc("too large","Very large image (corrupt?)");
+   if (s->img_x > STBI_MAX_DIMENSIONS) return stbi__errpuc("too large","Very large image (corrupt?)");
+
    *x = s->img_x;
    *y = s->img_y;
    if (comp) *comp = s->img_n;