[PATCH 8/8] ext4 crypto: allocate the right amount of memory for the on-disk symlink

Theodore Ts'o
2015-05-28T23:47:57Z

Previously we were taking the required padding when allocating space
for the on-disk symlink. This caused a buffer overrun which could
trigger a krenel crash when running fsstress.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
fs/ext4/crypto_fname.c | 25 +++++++++++++++----------
fs/ext4/ext4.h | 1 +
fs/ext4/namei.c | 32 +++++++++++++++++++++-----------
3 files changed, 37 insertions(+), 21 deletions(-)

diff --git a/fs/ext4/crypto_fname.c b/fs/ext4/crypto_fname.c
index 23af41f..7dc4eb5 100644
--- a/fs/ext4/crypto_fname.c
+++ b/fs/ext4/crypto_fname.c
@@ -262,8 +262,20 @@ u32 ext4_fname_crypto_round_up(u32 size, u32 blksize)
return ((size+blksize-1)/blksize)*blksize;
}

-/**
- * ext4_fname_crypto_alloc_obuff() -
+unsigned ext4_fname_encrypted_size(struct inode *inode, u32 ilen)
+{
+ struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
+ int padding = 32;
+
+ if (ci)
+ padding = 4 << (ci->ci_flags & EXT4_POLICY_FLAGS_PAD_MASK);
+ if (ilen < EXT4_CRYPTO_BLOCK_SIZE)
+ ilen = EXT4_CRYPTO_BLOCK_SIZE;
+ return ext4_fname_crypto_round_up(ilen, padding);
+}
+
+/*
+ * ext4_fname_crypto_alloc_buffer() -
*
* Allocates an output buffer that is sufficient for the crypto operation
* specified by the context and the direction.
@@ -271,15 +283,8 @@ u32 ext4_fname_crypto_round_up(u32 size, u32 blksize)
int ext4_fname_crypto_alloc_buffer(struct inode *inode,
u32 ilen, struct ext4_str *crypto_str)
{
- unsigned int olen;
- int padding = 16;
- struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
+ unsigned int olen = ext4_fname_encrypted_size(inode, ilen);

- if (ci)
- padding = 4 << (ci->ci_flags & EXT4_POLICY_FLAGS_PAD_MASK);
- if (padding < EXT4_CRYPTO_BLOCK_SIZE)
- padding = EXT4_CRYPTO_BLOCK_SIZE;
- olen = ext4_fname_crypto_round_up(ilen, padding);
crypto_str->len = olen;
if (olen < EXT4_FNAME_CRYPTO_DIGEST_SIZE*2)
olen = EXT4_FNAME_CRYPTO_DIGEST_SIZE*2;
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index bd8d32d..730c88d 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2090,6 +2090,7 @@ static inline int ext4_sb_has_crypto(struct super_block *sb)
/* crypto_fname.c */
bool ext4_valid_filenames_enc_mode(uint32_t mode);
u32 ext4_fname_crypto_round_up(u32 size, u32 blksize);
+unsigned ext4_fname_encrypted_size(struct inode *inode, u32 ilen);
int ext4_fname_crypto_alloc_buffer(struct inode *inode,
u32 ilen, struct ext4_str *crypto_str);
int _ext4_fname_disk_to_usr(struct inode *inode,
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 401b099..bda4a5d 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -3039,10 +3039,23 @@ static int ext4_symlink(struct inode *dir,

encryption_required = (ext4_encrypted_inode(dir) ||
DUMMY_ENCRYPTION_ENABLED(EXT4_SB(dir->i_sb)));
- if (encryption_required)
- disk_link.len = encrypted_symlink_data_len(len) + 1;
- if (disk_link.len > dir->i_sb->s_blocksize)
- return -ENAMETOOLONG;
+ if (encryption_required) {
+ err = ext4_get_encryption_info(dir);
+ if (err)
+ return err;
+ if (ext4_encryption_info(dir) == NULL)
+ return -EPERM;
+ disk_link.len = (ext4_fname_encrypted_size(dir, len) +
+ sizeof(struct ext4_encrypted_symlink_data));
+ sd = kzalloc(disk_link.len, GFP_KERNEL);
+ if (!sd)
+ return -ENOMEM;
+ }
+
+ if (disk_link.len > dir->i_sb->s_blocksize) {
+ err = -ENAMETOOLONG;
+ goto err_free_sd;
+ }

dquot_initialize(dir);

@@ -3073,18 +3086,14 @@ static int ext4_symlink(struct inode *dir,
if (IS_ERR(inode)) {
if (handle)
ext4_journal_stop(handle);
- return PTR_ERR(inode);
+ err = PTR_ERR(inode);
+ goto err_free_sd;
}

if (encryption_required) {
struct qstr istr;
struct ext4_str ostr;

- sd = kzalloc(disk_link.len, GFP_NOFS);
- if (!sd) {
- err = -ENOMEM;
- goto err_drop_inode;
- }
istr.name = (const unsigned char *) symname;
istr.len = len;
ostr.name = sd->encrypted_path;
@@ -3156,10 +3165,11 @@ static int ext4_symlink(struct inode *dir,
err_drop_inode:
if (handle)
ext4_journal_stop(handle);
- kfree(sd);
clear_nlink(inode);
unlock_new_inode(inode);
iput(inode);
+err_free_sd:
+ kfree(sd);
return err;
}

--
2.3.0