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tools lib api: Fix filename__write_int() writing uninitialized stack data

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filename__write_int() formats an integer into a 64-byte buffer with
sprintf() then passes sizeof(buf) (64) as the write length.  This
writes all 64 bytes including uninitialized stack data past the
formatted string.  Most sysfs files reject the oversized write,
making the function always return -1.

Fix by capturing the sprintf() return value and using it as the
write length.

Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Fixes: 3b00ea9386 ("tools lib api fs: Add sysfs__write_int function")
Cc: Kan Liang <kan.liang@intel.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Arnaldo Carvalho de Melo 2026-06-08 07:05:19 -03:00
parent 2ea64782a4
commit 438ece0618
1 changed files with 3 additions and 2 deletions
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5
tools/lib/api/fs/fs.c
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@ -376,12 +376,13 @@ int filename__write_int(const char *filename, int value)
{
int fd = open(filename, O_WRONLY), err = -1;
char buf[64];
int len;
if (fd < 0)
return -errno;
sprintf(buf, "%d", value);
if (write(fd, buf, sizeof(buf)) == sizeof(buf))
len = sprintf(buf, "%d", value);
if (write(fd, buf, len) == len)
err = 0;
close(fd);