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fgets: avoid arithmetic overflow when n==INT_MIN is passed

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performing n-- is not a safe operation for arbitrary signed input n.
only perform the decrement in the code path where the initial n is
greater than 1, and adjust the condition in the n<=1 code path to
compensate for it not having been decremented.
This commit is contained in:
Rich Felker 2022-10-07 19:37:56 -04:00
parent d8f35e29d0
commit 5ff3eea91f
1 changed files with 3 additions and 2 deletions
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5
src/stdio/fgets.c
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@ -12,13 +12,14 @@ char *fgets(char *restrict s, int n, FILE *restrict f)
FLOCK(f);
if (n--<=1) {
if (n<=1) {
f->mode |= f->mode-1;
FUNLOCK(f);
if (n) return 0;
if (n<1) return 0;
*s = 0;
return s;
}
n--;
while (n) {
if (f->rpos != f->rend) {