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 wthout 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 --- 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 160960bb0ad0..9ea3cd11dd93 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, "..", namelen)) { ino = rdt->parent_ino; } else if (rdt->cache) { struct ovl_cache_entry *p; -- 2.34.1