Re: [RESEND PATCH] btrfs: Fix UAF when cleaning up fs_devs with a single stale device
On Tue, Jan 30, 2018 at 04:07:37PM +0200, Nikolay Borisov wrote: > Commit 4fde46f0cc71 ("Btrfs: free the stale device") introduced > btrfs_free_stale_device which iterates the device lists for all > registered btrfs filesystems and deletes those devices which aren't > mounted. In a btrfs_devices structure has only 1 device attached to it > and it is unused then btrfs_free_stale_devices will proceed to also > free the btrfs_fs_devices struct itself. Currently this leads to a UAF > since list_for_each_entry will try to perform a check on the already- > freed memory to see if it has to terminated the loop. > > The fix is to use 'break' when we know we are freeing the current > fs_devs. > > Fixes: 4fde46f0cc71 ("Btrfs: free the stale device") > Signed-off-by: Nikolay BorisovAdded to next, thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[RESEND PATCH] btrfs: Fix UAF when cleaning up fs_devs with a single stale device
Commit 4fde46f0cc71 ("Btrfs: free the stale device") introduced btrfs_free_stale_device which iterates the device lists for all registered btrfs filesystems and deletes those devices which aren't mounted. In a btrfs_devices structure has only 1 device attached to it and it is unused then btrfs_free_stale_devices will proceed to also free the btrfs_fs_devices struct itself. Currently this leads to a UAF since list_for_each_entry will try to perform a check on the already- freed memory to see if it has to terminated the loop. The fix is to use 'break' when we know we are freeing the current fs_devs. Fixes: 4fde46f0cc71 ("Btrfs: free the stale device") Signed-off-by: Nikolay Borisov--- Changed the subject to make it more descriptive fs/btrfs/volumes.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index f7147740b68e..c3ab55336ee0 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -645,6 +645,7 @@ static void btrfs_free_stale_devices(const char *path, btrfs_sysfs_remove_fsid(fs_devs); list_del(_devs->list); free_fs_devices(fs_devs); + break; } else { fs_devs->num_devices--; list_del(>dev_list); -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] btrfs: Fix UAF
On 01/29/2018 03:01 PM, Nikolay Borisov wrote: On 29.01.2018 04:38, Anand Jain wrote: On 01/26/2018 09:20 PM, Nikolay Borisov wrote: Commit 4fde46f0cc71 ("Btrfs: free the stale device") introduced btrfs_free_stale_device which iterates the device lists for all registered btrfs filesystems and deletes those devices which aren't mounted. In a btrfs_devices structure has only 1 device attached to it and it is unused then btrfs_free_stale_devices will proceed to also free the btrfs_fs_devices struct itself. Currently this leads to a UAF since list_for_each_entry will try to perform a check on the already- freed memory to see if it has to terminated the loop. The fix is to use 'break' when we know we are freeing the current fs_devs. No break is needed as we need to iterate all stale devices and delete the found stale entry, so commit [1] used list_for_each_entry_safe() and removed the break, We only do the break if we know we have a single device in the current fs_devs struct. And executing free_fs_devices would have already freed the device + fs_devs. [1] commit 38cf665d338fca33af4b16f9ec7cad6637fc0fec Author: Anand Jainbtrfs: make btrfs_free_stale_device() to iterate all stales I am guessing UAF might be in[2], instead ? [2] free_fs_devices(fs_devs) :: while (!list_empty(_devices->devices)) { device = list_entry(fs_devices->devices.next, struct btrfs_device, dev_list); It's not that, I thought so at first. But here using list_empty you are awlays accessing the head the of the list, which is guaranteed to be valid since you do the freeing of fs_devices outside of the while loop. break when num_devices == 1 is fine; Reviewed-by: Anand Jain Thanks, Anand Thanks, Anand Fixes: 4fde46f0cc71 ("Btrfs: free the stale device") Signed-off-by: Nikolay Borisov --- fs/btrfs/volumes.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index f7147740b68e..c3ab55336ee0 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -645,6 +645,7 @@ static void btrfs_free_stale_devices(const char *path, btrfs_sysfs_remove_fsid(fs_devs); list_del(_devs->list); free_fs_devices(fs_devs); + break; } else { fs_devs->num_devices--; list_del(>dev_list); -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] btrfs: Fix UAF
On 29.01.2018 04:38, Anand Jain wrote: > > > On 01/26/2018 09:20 PM, Nikolay Borisov wrote: >> Commit 4fde46f0cc71 ("Btrfs: free the stale device") introduced >> btrfs_free_stale_device which iterates the device lists for all >> registered btrfs filesystems and deletes those devices which aren't >> mounted. In a btrfs_devices structure has only 1 device attached to it >> and it is unused then btrfs_free_stale_devices will proceed to also >> free the btrfs_fs_devices struct itself. Currently this leads to a UAF >> since list_for_each_entry will try to perform a check on the already- >> freed memory to see if it has to terminated the loop. >> >> The fix is to use 'break' when we know we are freeing the current >> fs_devs. > > No break is needed as we need to iterate all stale devices and delete > the found stale entry, so commit [1] used list_for_each_entry_safe() > and removed the break, We only do the break if we know we have a single device in the current fs_devs struct. And executing free_fs_devices would have already freed the device + fs_devs. > > [1] > commit 38cf665d338fca33af4b16f9ec7cad6637fc0fec > Author: Anand Jain> btrfs: make btrfs_free_stale_device() to iterate all stales > > > I am guessing UAF might be in[2], instead ? > > [2] > free_fs_devices(fs_devs) > :: > while (!list_empty(_devices->devices)) { > device = list_entry(fs_devices->devices.next, > struct btrfs_device, dev_list); It's not that, I thought so at first. But here using list_empty you are awlays accessing the head the of the list, which is guaranteed to be valid since you do the freeing of fs_devices outside of the while loop. > > Thanks, Anand > >> Fixes: 4fde46f0cc71 ("Btrfs: free the stale device") >> Signed-off-by: Nikolay Borisov >> >> --- >> fs/btrfs/volumes.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c >> index f7147740b68e..c3ab55336ee0 100644 >> --- a/fs/btrfs/volumes.c >> +++ b/fs/btrfs/volumes.c >> @@ -645,6 +645,7 @@ static void btrfs_free_stale_devices(const char >> *path, >> btrfs_sysfs_remove_fsid(fs_devs); >> list_del(_devs->list); >> free_fs_devices(fs_devs); >> + break; >> } else { >> fs_devs->num_devices--; >> list_del(>dev_list); >> > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] btrfs: Fix UAF
On 01/26/2018 09:20 PM, Nikolay Borisov wrote: Commit 4fde46f0cc71 ("Btrfs: free the stale device") introduced btrfs_free_stale_device which iterates the device lists for all registered btrfs filesystems and deletes those devices which aren't mounted. In a btrfs_devices structure has only 1 device attached to it and it is unused then btrfs_free_stale_devices will proceed to also free the btrfs_fs_devices struct itself. Currently this leads to a UAF since list_for_each_entry will try to perform a check on the already- freed memory to see if it has to terminated the loop. The fix is to use 'break' when we know we are freeing the current fs_devs. No break is needed as we need to iterate all stale devices and delete the found stale entry, so commit [1] used list_for_each_entry_safe() and removed the break, [1] commit 38cf665d338fca33af4b16f9ec7cad6637fc0fec Author: Anand Jainbtrfs: make btrfs_free_stale_device() to iterate all stales I am guessing UAF might be in[2], instead ? [2] free_fs_devices(fs_devs) :: while (!list_empty(_devices->devices)) { device = list_entry(fs_devices->devices.next, struct btrfs_device, dev_list); Thanks, Anand Fixes: 4fde46f0cc71 ("Btrfs: free the stale device") Signed-off-by: Nikolay Borisov > --- fs/btrfs/volumes.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index f7147740b68e..c3ab55336ee0 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -645,6 +645,7 @@ static void btrfs_free_stale_devices(const char *path, btrfs_sysfs_remove_fsid(fs_devs); list_del(_devs->list); free_fs_devices(fs_devs); + break; } else { fs_devs->num_devices--; list_del(>dev_list); -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH] btrfs: Fix UAF
Commit 4fde46f0cc71 ("Btrfs: free the stale device") introduced btrfs_free_stale_device which iterates the device lists for all registered btrfs filesystems and deletes those devices which aren't mounted. In a btrfs_devices structure has only 1 device attached to it and it is unused then btrfs_free_stale_devices will proceed to also free the btrfs_fs_devices struct itself. Currently this leads to a UAF since list_for_each_entry will try to perform a check on the already- freed memory to see if it has to terminated the loop. The fix is to use 'break' when we know we are freeing the current fs_devs. Fixes: 4fde46f0cc71 ("Btrfs: free the stale device") Signed-off-by: Nikolay Borisov--- fs/btrfs/volumes.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index f7147740b68e..c3ab55336ee0 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -645,6 +645,7 @@ static void btrfs_free_stale_devices(const char *path, btrfs_sysfs_remove_fsid(fs_devs); list_del(_devs->list); free_fs_devices(fs_devs); + break; } else { fs_devs->num_devices--; list_del(>dev_list); -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html