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authorEric Biggers <ebiggers@google.com>2021-07-02 09:53:46 +0300
committerEric Biggers <ebiggers@google.com>2021-07-26 06:01:06 +0300
commitd18760560593e5af921f51a8c9b64b6109d634c2 (patch)
tree759071b570d7dfd6b634d3364a20a7c033baab23 /include/linux/fscrypt.h
parentff1176468d368232b684f75e82563369208bc371 (diff)
downloadlinux-d18760560593e5af921f51a8c9b64b6109d634c2.tar.xz
fscrypt: add fscrypt_symlink_getattr() for computing st_size
Add a helper function fscrypt_symlink_getattr() which will be called from the various filesystems' ->getattr() methods to read and decrypt the target of encrypted symlinks in order to report the correct st_size. Detailed explanation: As required by POSIX and as documented in various man pages, st_size for a symlink is supposed to be the length of the symlink target. Unfortunately, st_size has always been wrong for encrypted symlinks because st_size is populated from i_size from disk, which intentionally contains the length of the encrypted symlink target. That's slightly greater than the length of the decrypted symlink target (which is the symlink target that userspace usually sees), and usually won't match the length of the no-key encoded symlink target either. This hadn't been fixed yet because reporting the correct st_size would require reading the symlink target from disk and decrypting or encoding it, which historically has been considered too heavyweight to do in ->getattr(). Also historically, the wrong st_size had only broken a test (LTP lstat03) and there were no known complaints from real users. (This is probably because the st_size of symlinks isn't used too often, and when it is, typically it's for a hint for what buffer size to pass to readlink() -- which a slightly-too-large size still works for.) However, a couple things have changed now. First, there have recently been complaints about the current behavior from real users: - Breakage in rpmbuild: https://github.com/rpm-software-management/rpm/issues/1682 https://github.com/google/fscrypt/issues/305 - Breakage in toybox cpio: https://www.mail-archive.com/toybox@lists.landley.net/msg07193.html - Breakage in libgit2: https://issuetracker.google.com/issues/189629152 (on Android public issue tracker, requires login) Second, we now cache decrypted symlink targets in ->i_link. Therefore, taking the performance hit of reading and decrypting the symlink target in ->getattr() wouldn't be as big a deal as it used to be, since usually it will just save having to do the same thing later. Also note that eCryptfs ended up having to read and decrypt symlink targets in ->getattr() as well, to fix this same issue; see commit 3a60a1686f0d ("eCryptfs: Decrypt symlink target for stat size"). So, let's just bite the bullet, and read and decrypt the symlink target in ->getattr() in order to report the correct st_size. Add a function fscrypt_symlink_getattr() which the filesystems will call to do this. (Alternatively, we could store the decrypted size of symlinks on-disk. But there isn't a great place to do so, and encryption is meant to hide the original size to some extent; that property would be lost.) Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20210702065350.209646-2-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'include/linux/fscrypt.h')
-rw-r--r--include/linux/fscrypt.h7
1 files changed, 7 insertions, 0 deletions
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 2ea1387bb497..b7bfd0cd4f3e 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -253,6 +253,7 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
unsigned int max_size,
struct delayed_call *done);
+int fscrypt_symlink_getattr(const struct path *path, struct kstat *stat);
static inline void fscrypt_set_ops(struct super_block *sb,
const struct fscrypt_operations *s_cop)
{
@@ -583,6 +584,12 @@ static inline const char *fscrypt_get_symlink(struct inode *inode,
return ERR_PTR(-EOPNOTSUPP);
}
+static inline int fscrypt_symlink_getattr(const struct path *path,
+ struct kstat *stat)
+{
+ return -EOPNOTSUPP;
+}
+
static inline void fscrypt_set_ops(struct super_block *sb,
const struct fscrypt_operations *s_cop)
{