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SubjectRe: [PATCH v3 1/1] ovl: setxattr: don't deadlock when called from ima_fix_xattr.
On Fri, May 20, 2016 at 11:53:18PM +0300, Krisztian Litkey wrote:
> On Fri, May 20, 2016 at 8:00 PM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:

> > We deferred __fput() back in 2012 in order for IMA to safely take the
> > i_mutex and write security.ima. Writing the security.ima xattr now
> > triggers overlayfs to write the xattr, but overlayfs doesn't
> > differentiate between callers - as a result of userspace or as described
> > here in __fput(). All calls to ovl_setxattr() should call vfs_sexattr,
> > except the one triggered by __fput(). Refer to the original lockdep
> > report -
> > http://thread.gmane.org/gmane.linux.file-systems.union/640

Looks like more fallout from 4bacc9c9234c ("overlayfs: Make f_path always point
to the overlay and f_inode to the underlay").

Not sure what we want here. Doing everything on the underlying dentry/inode
would be trivial (see attached patch).

Question is, can we get setxattr() on file opened for O_RDONLY? If so, then
that could fail on overlayfs (lower layer is read-only).

Thanks,
Miklos

---
From: Miklos Szeredi <mszeredi@redhat.com>
Subject: ima: use file_path()

Ima tries to call ->setxattr() on overlayfs dentry after having locked
underlying inode, which results in a deadlock.

Reported-by: Krisztian Litkey <kli@iki.fi>
Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org> # v4.2
---
security/integrity/ima/ima_appraise.c | 4 ++--
security/integrity/ima/ima_main.c | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)

--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -222,7 +222,7 @@ static int process_measurement(struct fi
if ((action & IMA_APPRAISE_SUBMASK) ||
strcmp(template_desc->name, IMA_TEMPLATE_IMA_NAME) != 0)
/* read 'security.ima' */
- xattr_len = ima_read_xattr(file->f_path.dentry, &xattr_value);
+ xattr_len = ima_read_xattr(file_dentry(file), &xattr_value);

hash_algo = ima_get_hash_algo(xattr_value, xattr_len);

--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -190,7 +190,7 @@ int ima_appraise_measurement(enum ima_ho
{
static const char op[] = "appraise_data";
char *cause = "unknown";
- struct dentry *dentry = file->f_path.dentry;
+ struct dentry *dentry = file_dentry(file);
struct inode *inode = d_backing_inode(dentry);
enum integrity_status status = INTEGRITY_UNKNOWN;
int rc = xattr_len, hash_start = 0;
@@ -295,7 +295,7 @@ int ima_appraise_measurement(enum ima_ho
*/
void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
{
- struct dentry *dentry = file->f_path.dentry;
+ struct dentry *dentry = file_dentry(file);
int rc = 0;

/* do not collect and update hash for digital signatures */
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