From 438ece06185696e14c63c6113d5e2d34ec0a9680 Mon Sep 17 00:00:00 2001 From: Arnaldo Carvalho de Melo Date: Mon, 8 Jun 2026 07:05:19 -0300 Subject: [PATCH] tools lib api: Fix filename__write_int() writing uninitialized stack data 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 Fixes: 3b00ea938653d136 ("tools lib api fs: Add sysfs__write_int function") Cc: Kan Liang Assisted-by: Claude:claude-opus-4.6 Signed-off-by: Arnaldo Carvalho de Melo --- tools/lib/api/fs/fs.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/tools/lib/api/fs/fs.c b/tools/lib/api/fs/fs.c index 3cc302d4c47b1..d16911818d4d3 100644 --- a/tools/lib/api/fs/fs.c +++ b/tools/lib/api/fs/fs.c @@ -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); -- 2.47.3