Messages in this thread Patch in this message | | | Date | Wed, 22 Oct 2008 12:14:00 -0500 | From | Eric Sandeen <> | Subject | [PATCH] 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 7fcba054373d5dfc43d26e243a5c9b92069972ee)
Signed-off-by: Eric Sandeen <sandeen@redhat.com> ---
Index: linux-2.6.27.x86_64/fs/ecryptfs/crypto.c =================================================================== --- linux-2.6.27.x86_64.orig/fs/ecryptfs/crypto.c +++ linux-2.6.27.x86_64/fs/ecryptfs/crypto.c @@ -1251,6 +1251,7 @@ struct kmem_cache *ecryptfs_header_cache /** * 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 * * 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(c 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 dentr 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 dentr 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; }
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