From: Eric Biggers <ebiggers@kernel.org>
To: linux-f2fs-devel@lists.sourceforge.net
Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
Daniel Rosenberg <drosen@google.com>,
Gabriel Krisman Bertazi <krisman@collabora.com>
Subject: [PATCH 2/2] f2fs: fix race conditions in ->d_compare() and ->d_hash()
Date: Thu, 23 Jan 2020 20:15:49 -0800 [thread overview]
Message-ID: <20200124041549.159983-3-ebiggers@kernel.org> (raw)
In-Reply-To: <20200124041549.159983-1-ebiggers@kernel.org>
From: Eric Biggers <ebiggers@google.com>
Since ->d_compare() and ->d_hash() can be called in RCU-walk mode,
->d_parent and ->d_inode can be concurrently modified, and in
particular, ->d_inode may be changed to NULL. For f2fs_d_hash() this
resulted in a reproducible NULL dereference if a lookup is done in a
directory being deleted, e.g. with:
int main()
{
if (fork()) {
for (;;) {
mkdir("subdir", 0700);
rmdir("subdir");
}
} else {
for (;;)
access("subdir/file", 0);
}
}
... or by running the 't_encrypted_d_revalidate' program from xfstests.
Both repros work in any directory on a filesystem with the encoding
feature, even if the directory doesn't actually have the casefold flag.
I couldn't reproduce a crash in f2fs_d_compare(), but it appears that a
similar crash is possible there.
Fix these bugs by reading ->d_parent and ->d_inode using READ_ONCE() and
falling back to the case sensitive behavior if the inode is NULL.
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Fixes: 2c2eb7a300cd ("f2fs: Support case-insensitive file name lookups")
Cc: <stable@vger.kernel.org> # v5.4+
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
fs/f2fs/dir.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index aea9e2806144d..d7c9a2cda4899 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -1083,24 +1083,27 @@ static int f2fs_d_compare(const struct dentry *dentry, unsigned int len,
const char *str, const struct qstr *name)
{
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);
- if (!IS_CASEFOLDED(dentry->d_parent->d_inode)) {
+ if (!inode || !IS_CASEFOLDED(inode)) {
if (len != name->len)
return -1;
return memcmp(str, name->name, len);
}
- return f2fs_ci_compare(dentry->d_parent->d_inode, name, &qstr, false);
+ return f2fs_ci_compare(inode, name, &qstr, false);
}
static int f2fs_d_hash(const struct dentry *dentry, struct qstr *str)
{
struct f2fs_sb_info *sbi = F2FS_SB(dentry->d_sb);
const struct unicode_map *um = sbi->s_encoding;
+ const struct inode *inode = READ_ONCE(dentry->d_inode);
unsigned char *norm;
int len, ret = 0;
- if (!IS_CASEFOLDED(dentry->d_inode))
+ if (!inode || !IS_CASEFOLDED(inode))
return 0;
norm = f2fs_kmalloc(sbi, PATH_MAX, GFP_ATOMIC);
--
2.25.0
prev parent reply other threads:[~2020-01-24 4:16 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-24 4:15 [PATCH 0/2] f2fs: fixes for f2fs_d_compare() and f2fs_d_hash() Eric Biggers
2020-01-24 4:15 ` [PATCH 1/2] f2fs: fix dcache lookup of !casefolded directories Eric Biggers
2020-01-24 4:15 ` Eric Biggers [this message]
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