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ecryptfs: fix memory corruption when storing crypto info in xattrs

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When ecryptfs allocates space to write crypto headers into, before copying
it out to file headers or to xattrs, it looks at the value of
crypt_stat->num_header_bytes_at_front to determine how much space it
needs.  This is also used as the file offset to the actual encrypted data,
so for xattr-stored crypto info, the value was zero.

So, we kzalloc'd 0 bytes, and then ran off to write to that memory.
(Which returned as ZERO_SIZE_PTR, so we explode quickly).

The right answer is to always allocate a page to write into; the current
code won't ever write more than that (this is enforced by the
(PAGE_CACHE_SIZE - offset) length in the call to
ecryptfs_generate_key_packet_set).  To be explicit about this, we now send
in a "max" parameter, rather than magically using PAGE_CACHE_SIZE there.

Also, since the pointer we pass down the callchain eventually gets the
virt_to_page() treatment, we should be using a alloc_page variant, not
kzalloc (see also 7fcba05437)

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Acked-by: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Eric Sandeen 2008-10-29 14:01:08 -07:00 committed by Linus Torvalds
parent ce05fcc30e
commit 87b811c3f9
1 changed files with 8 additions and 7 deletions
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15
fs/ecryptfs/crypto.c
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@ -1251,6 +1251,7 @@ struct kmem_cache *ecryptfs_header_cache_2;
/**
* ecryptfs_write_headers_virt
* @page_virt: The virtual address to write the headers to
* @max: The size of memory allocated at page_virt
* @size: Set to the number of bytes written by this function
* @crypt_stat: The cryptographic context
* @ecryptfs_dentry: The eCryptfs dentry
@ -1278,7 +1279,8 @@ struct kmem_cache *ecryptfs_header_cache_2;
*
* Returns zero on success
*/
static int ecryptfs_write_headers_virt(char *page_virt, size_t *size,
static int ecryptfs_write_headers_virt(char *page_virt, size_t max,
size_t *size,
struct ecryptfs_crypt_stat *crypt_stat,
struct dentry *ecryptfs_dentry)
{
@ -1296,7 +1298,7 @@ static int ecryptfs_write_headers_virt(char *page_virt, size_t *size,
offset += written;
rc = ecryptfs_generate_key_packet_set((page_virt + offset), crypt_stat,
ecryptfs_dentry, &written,
PAGE_CACHE_SIZE - offset);
max - offset);
if (rc)
ecryptfs_printk(KERN_WARNING, "Error generating key packet "
"set; rc = [%d]\n", rc);
@ -1368,14 +1370,14 @@ int ecryptfs_write_metadata(struct dentry *ecryptfs_dentry)
goto out;
}
/* Released in this function */
virt = kzalloc(crypt_stat->num_header_bytes_at_front, GFP_KERNEL);
virt = (char *)get_zeroed_page(GFP_KERNEL);
if (!virt) {
printk(KERN_ERR "%s: Out of memory\n", __func__);
rc = -ENOMEM;
goto out;
}
rc = ecryptfs_write_headers_virt(virt, &size, crypt_stat,
ecryptfs_dentry);
rc = ecryptfs_write_headers_virt(virt, PAGE_CACHE_SIZE, &size,
crypt_stat, ecryptfs_dentry);
if (unlikely(rc)) {
printk(KERN_ERR "%s: Error whilst writing headers; rc = [%d]\n",
__func__, rc);
@ -1393,8 +1395,7 @@ int ecryptfs_write_metadata(struct dentry *ecryptfs_dentry)
goto out_free;
}
out_free:
memset(virt, 0, crypt_stat->num_header_bytes_at_front);
kfree(virt);
free_page((unsigned long)virt);
out:
return rc;
}