[PATCH 6.19 597/781] ovl: Fix uninit-value in ovl_fill_real

Greg Kroah-Hartman
2026-02-25T01:38:04Z

From: Qing Wang <wangqing7171@gmail.com>

[ Upstream commit 1992330d90dd766fcf1730fd7bf2d6af65370ac4 ]

Syzbot reported a KMSAN uninit-value issue in ovl_fill_real.

This iusse's call chain is:
__do_sys_getdents64()
-> iterate_dir()
...
-> ext4_readdir()
-> fscrypt_fname_alloc_buffer() // alloc
-> fscrypt_fname_disk_to_usr // write without tail '\0'
-> dir_emit()
-> ovl_fill_real() // read by strcmp()

The string is used to store the decrypted directory entry name for an
encrypted inode. As shown in the call chain, fscrypt_fname_disk_to_usr()
write it without null-terminate. However, ovl_fill_real() uses strcmp() to
compare the name against "..", which assumes a null-terminated string and
may trigger a KMSAN uninit-value warning when the buffer tail contains
uninit data.

Reported-by: syzbot+d130f98b2c265fae5297@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=d130f98b2c265fae5297
Fixes: 4edb83bb1041 ("ovl: constant d_ino for non-merge dirs")
Signed-off-by: Qing Wang <wangqing7171@gmail.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://patch.msgid.link/20260128132406.23768-2-amir73il@gmail.com
Acked-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/overlayfs/readdir.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 160960bb0ad0b..724ec9d93fc82 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -755,7 +755,7 @@ static bool ovl_fill_real(struct dir_context *ctx, const char *name,
struct dir_context *orig_ctx = rdt->orig_ctx;
bool res;

- if (rdt->parent_ino && strcmp(name, "..") == 0) {
+ if (rdt->parent_ino && namelen == 2 && !strncmp(name, "..", 2)) {
ino = rdt->parent_ino;
} else if (rdt->cache) {
struct ovl_cache_entry *p;
--
2.51.0