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ext4: fix race conditions in ->d_compare() and ->d_hash()
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 ext4_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 ext4_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: b886ee3e77
("ext4: Support case-insensitive file name lookups")
Cc: <stable@vger.kernel.org> # v5.2+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20200124041234.159740-1-ebiggers@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
parent
244adf6426
commit
ec772f0130
1 changed files with 6 additions and 3 deletions
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@ -671,9 +671,11 @@ static int ext4_d_compare(const struct dentry *dentry, unsigned int len,
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const char *str, const struct qstr *name)
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{
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struct qstr qstr = {.name = str, .len = len };
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struct inode *inode = dentry->d_parent->d_inode;
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const struct dentry *parent = READ_ONCE(dentry->d_parent);
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const struct inode *inode = READ_ONCE(parent->d_inode);
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if (!IS_CASEFOLDED(inode) || !EXT4_SB(inode->i_sb)->s_encoding) {
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if (!inode || !IS_CASEFOLDED(inode) ||
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!EXT4_SB(inode->i_sb)->s_encoding) {
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if (len != name->len)
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return -1;
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return memcmp(str, name->name, len);
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@ -686,10 +688,11 @@ static int ext4_d_hash(const struct dentry *dentry, struct qstr *str)
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{
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const struct ext4_sb_info *sbi = EXT4_SB(dentry->d_sb);
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const struct unicode_map *um = sbi->s_encoding;
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const struct inode *inode = READ_ONCE(dentry->d_inode);
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unsigned char *norm;
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int len, ret = 0;
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if (!IS_CASEFOLDED(dentry->d_inode) || !um)
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if (!inode || !IS_CASEFOLDED(inode) || !um)
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return 0;
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norm = kmalloc(PATH_MAX, GFP_ATOMIC);
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