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avoid updating caller's size when getdelim fails to realloc 

getdelim was updating *n, the caller's stored buffer size, before
calling realloc. if getdelim then failed due to realloc failure, the
caller would see in *n a value larger than the actual size of the
allocated block, and use of that value is unsafe. in particular,
passing it again to getdelim is unsafe.

now, temporary storage is used for the desired new size, and *n is not
written until realloc succeeds.
This commit is contained in:
Rich Felker 2015-12-19 23:43:31 -05:00
parent 42216742cd
commit d87f0a9a95
1 changed files with 6 additions and 5 deletions
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11
src/stdio/getdelim.c
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@ -29,15 +29,16 @@ ssize_t getdelim(char **restrict s, size_t *restrict n, int delim, FILE *restric
k = z ? z - f->rpos + 1 : f->rend - f->rpos;
if (i+k+1 >= *n) {
if (k >= SIZE_MAX/2-i) goto oom;
*n = i+k+2;
if (*n < SIZE_MAX/4) *n *= 2;
tmp = realloc(*s, *n);
size_t m = i+k+2;
if (m < SIZE_MAX/4) m *= 2;
tmp = realloc(*s, m);
if (!tmp) {
*n = i+k+2;
tmp = realloc(*s, *n);
m = i+k+2;
tmp = realloc(*s, m);
if (!tmp) goto oom;
}
*s = tmp;
*n = m;
}
memcpy(*s+i, f->rpos, k);
f->rpos += k;