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Commit 47512299 authored by Eric Biggers's avatar Eric Biggers Committed by Jaegeuk Kim
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f2fs: avoid utf8_strncasecmp() with unstable name 



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: <stable@vger.kernel.org> # v5.4+
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Daniel Rosenberg <drosen@google.com>
Cc: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
Reviewed-by: default avatarChao Yu <yuchao0@huawei.com>
Signed-off-by: default avatarJaegeuk Kim <jaegeuk@kernel.org>
parent d17c0c64

fs/f2fs/dir.c

+16 −0
Original line number Diff line number Diff line
@@ -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;

		entry.name = strbuf;

		/* prevent compiler from optimizing out the temporary buffer */

		barrier();

	}



	res = utf8_strncasecmp(sbi->s_encoding, name, &entry);

	if (res >= 0)

		return res;