lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Date:   Mon,  1 Jun 2020 13:08:05 -0700
From:   Eric Biggers <>
Cc:, Daniel Rosenberg <>,, Al Viro <>,,
        Gabriel Krisman Bertazi <>
Subject: [PATCH v2] f2fs: avoid utf8_strncasecmp() with unstable name

From: Eric Biggers <>

If the dentry name passed to ->d_compare() fits in dentry::d_iname, then
it may be concurrently modified by a rename.  This can cause undefined
behavior (possibly out-of-bounds memory accesses or crashes) in
utf8_strncasecmp(), since fs/unicode/ isn't written to handle strings
that may be concurrently modified.

Fix this by first copying the filename to a stack buffer if needed.
This way we get a stable snapshot of the filename.

Fixes: 2c2eb7a300cd ("f2fs: Support case-insensitive file name lookups")
Cc: <> # v5.4+
Cc: Al Viro <>
Cc: Daniel Rosenberg <>
Cc: Gabriel Krisman Bertazi <>
Signed-off-by: Eric Biggers <>

v2: Use memcpy() + barrier() instead of a byte-by-byte copy.
    Also rebased onto f2fs/dev.

 fs/f2fs/dir.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index 29f70f2295cce..d35976785e8c5 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -1114,11 +1114,27 @@ static int f2fs_d_compare(const struct dentry *dentry, unsigned int len,
 	const struct inode *dir = READ_ONCE(parent->d_inode);
 	const struct f2fs_sb_info *sbi = F2FS_SB(dentry->d_sb);
 	struct qstr entry = QSTR_INIT(str, len);
+	char strbuf[DNAME_INLINE_LEN];
 	int res;
 	if (!dir || !IS_CASEFOLDED(dir))
 		goto fallback;
+	/*
+	 * If the dentry name is stored in-line, then it may be concurrently
+	 * modified by a rename.  If this happens, the VFS will eventually retry
+	 * the lookup, so it doesn't matter what ->d_compare() returns.
+	 * However, it's unsafe to call utf8_strncasecmp() with an unstable
+	 * string.  Therefore, we have to copy the name into a temporary buffer.
+	 */
+	if (len <= DNAME_INLINE_LEN - 1) {
+		memcpy(strbuf, str, len);
+		strbuf[len] = 0;
+ = strbuf;
+		/* prevent compiler from optimizing out the temporary buffer */
+		barrier();
+	}
 	res = utf8_strncasecmp(sbi->s_encoding, name, &entry);
 	if (res >= 0)
 		return res;

Powered by blists - more mailing lists