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[2001:1c00:570d:ee00:c84e:f30e:bdab:df5a]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b8dbf184343sm122306466b.33.2026.01.28.05.24.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Jan 2026 05:24:08 -0800 (PST) From: Amir Goldstein To: Miklos Szeredi , Christian Brauner Cc: Qing Wang , linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org, syzbot+d130f98b2c265fae5297@syzkaller.appspotmail.com Subject: [PATCH 1/3] ovl: Fix uninit-value in ovl_fill_real Date: Wed, 28 Jan 2026 14:24:04 +0100 Message-ID: <20260128132406.23768-2-amir73il@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260128132406.23768-1-amir73il@gmail.com> References: <20260128132406.23768-1-amir73il@gmail.com> Precedence: bulk X-Mailing-List: linux-unionfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Qing Wang 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 Signed-off-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 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; -- 2.52.0