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Tue, 27 Jan 2026 02:52:55 -0800 (PST) From: Qing Wang To: miklos@szeredi.hu Cc: amir73il@gmail.com, linux-kernel@vger.kernel.org, linux-unionfs@vger.kernel.org, syzbot+d130f98b2c265fae5297@syzkaller.appspotmail.com, wangqing7171@gmail.com Subject: [PATCH v2] ovl: Fix uninit-value in ovl_fill_real Date: Tue, 27 Jan 2026 18:52:48 +0800 Message-Id: <20260127105248.1485922-1-wangqing7171@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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=3Dd130f98b2c265fae5297 Fixes: 4edb83bb1041 ("ovl: constant d_ino for non-merge dirs") Signed-off-by: Qing Wang Reviewed-by: Amir Goldstein --- 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, cons= t char *name, struct dir_context *orig_ctx =3D rdt->orig_ctx; bool res; =20 - if (rdt->parent_ino && strcmp(name, "..") =3D=3D 0) { + if (rdt->parent_ino && namelen =3D=3D 2 && !strncmp(name, "..", namelen))= { ino =3D rdt->parent_ino; } else if (rdt->cache) { struct ovl_cache_entry *p; --=20 2.34.1