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fsverity updates for 5.9

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One fix for fs/verity/ to strengthen a memory barrier which might be too
 weak.  This mirrors a similar fix in fs/crypto/.
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Merge tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt

Pull fsverity update from Eric Biggers:
 "One fix for fs/verity/ to strengthen a memory barrier which might be
  too weak. This mirrors a similar fix in fs/crypto/"

* tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fscrypt/fscrypt:
  fs-verity: use smp_load_acquire() for ->i_verity_info
This commit is contained in:
Linus Torvalds 2020-08-03 10:19:35 -07:00
commit 5577416c39
2 changed files with 19 additions and 5 deletions
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15
fs/verity/open.c
View File

@ -221,11 +221,20 @@ out:
void fsverity_set_info(struct inode *inode, struct fsverity_info *vi)
{
/*
* Multiple processes may race to set ->i_verity_info, so use cmpxchg.
* This pairs with the READ_ONCE() in fsverity_get_info().
* Multiple tasks may race to set ->i_verity_info, so use
* cmpxchg_release(). This pairs with the smp_load_acquire() in
* fsverity_get_info(). I.e., here we publish ->i_verity_info with a
* RELEASE barrier so that other tasks can ACQUIRE it.
*/
if (cmpxchg(&inode->i_verity_info, NULL, vi) != NULL)
if (cmpxchg_release(&inode->i_verity_info, NULL, vi) != NULL) {
/* Lost the race, so free the fsverity_info we allocated. */
fsverity_free_info(vi);
/*
* Afterwards, the caller may access ->i_verity_info directly,
* so make sure to ACQUIRE the winning fsverity_info.
*/
(void)fsverity_get_info(inode);
}
}
void fsverity_free_info(struct fsverity_info *vi)

9
include/linux/fsverity.h
View File

@ -115,8 +115,13 @@ struct fsverity_operations {
static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
{
/* pairs with the cmpxchg() in fsverity_set_info() */
return READ_ONCE(inode->i_verity_info);
/*
* Pairs with the cmpxchg_release() in fsverity_set_info().
* I.e., another task may publish ->i_verity_info concurrently,
* executing a RELEASE barrier. We need to use smp_load_acquire() here
* to safely ACQUIRE the memory the other task published.
*/
return smp_load_acquire(&inode->i_verity_info);
}
/* enable.c */