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Message-Id: <20200601200805.59655-1-ebiggers@kernel.org> Date: Mon, 1 Jun 2020 13:08:05 -0700 From: Eric Biggers <ebiggers@...nel.org> To: linux-f2fs-devel@...ts.sourceforge.net Cc: linux-ext4@...r.kernel.org, Daniel Rosenberg <drosen@...gle.com>, stable@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org, Gabriel Krisman Bertazi <krisman@...labora.co.uk> Subject: [PATCH v2] f2fs: avoid utf8_strncasecmp() with unstable name From: Eric Biggers <ebiggers@...gle.com> 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@...r.kernel.org> # v5.4+ Cc: Al Viro <viro@...iv.linux.org.uk> Cc: Daniel Rosenberg <drosen@...gle.com> Cc: Gabriel Krisman Bertazi <krisman@...labora.co.uk> Signed-off-by: Eric Biggers <ebiggers@...gle.com> --- 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; + 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; -- 2.26.2
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