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Be more aggressive about unexpected EOF conditions. 

Fixes several hangs in the presence of bad input data.
This commit is contained in:
Ryan C. Gordon 2020-04-28 10:39:47 -04:00
parent eb4b057f0d
commit 95560bc6cf
1 changed files with 17 additions and 4 deletions
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21
stb_image.h
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@ -4039,16 +4039,23 @@ 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);
@ -4085,7 +4092,12 @@ 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;
@ -4255,6 +4267,7 @@ 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