From: Eric Biggers <ebiggers@kernel.org>
To: linux-f2fs-devel@lists.sourceforge.net
Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
stable@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>,
Daniel Rosenberg <drosen@google.com>,
Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Subject: [PATCH] f2fs: avoid utf8_strncasecmp() with unstable name
Date: Fri, 29 May 2020 23:04:18 -0700 [thread overview]
Message-ID: <20200530060418.221707-1-ebiggers@kernel.org> (raw)
From: Eric Biggers <ebiggers@google.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@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: Eric Biggers <ebiggers@google.com>
---
fs/f2fs/dir.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index 44bfc464df787..5c179b72eb8a8 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -1083,6 +1083,7 @@ static int f2fs_d_compare(const struct dentry *dentry, unsigned int len,
struct qstr qstr = {.name = str, .len = len };
const struct dentry *parent = READ_ONCE(dentry->d_parent);
const struct inode *inode = READ_ONCE(parent->d_inode);
+ char strbuf[DNAME_INLINE_LEN];
if (!inode || !IS_CASEFOLDED(inode)) {
if (len != name->len)
@@ -1090,6 +1091,22 @@ static int f2fs_d_compare(const struct dentry *dentry, unsigned int len,
return memcmp(str, name->name, len);
}
+ /*
+ * 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) {
+ unsigned int i;
+
+ for (i = 0; i < len; i++)
+ strbuf[i] = READ_ONCE(str[i]);
+ strbuf[len] = 0;
+ qstr.name = strbuf;
+ }
+
return f2fs_ci_compare(inode, name, &qstr, false);
}
--
2.26.2
next reply other threads:[~2020-05-30 6:04 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-30 6:04 Eric Biggers [this message]
2020-05-30 15:07 ` [PATCH] f2fs: avoid utf8_strncasecmp() with unstable name Jaegeuk Kim
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