On Thu, Oct 12, 2023 at 06:04:30PM +0100, Lorenzo Stoakes wrote:
> In order for a F_SEAL_WRITE sealed memfd mapping to have an opportunity to
> clear VM_MAYWRITE, we must be able to invoke the appropriate vm_ops->mmap()
> handler to do so. We would otherwise fail the mapping_map_writable() check
> before we had the opportunity to avoid it.
>
> This patch moves this check after the call_mmap() invocation. Only memfd
> actively denies write access causing a potential failure here (in
> memfd_add_seals()), so there should be no impact on non-memfd cases.
>
> This patch makes the userland-visible change that MAP_SHARED, PROT_READ
> mappings of an F_SEAL_WRITE sealed memfd mapping will now succeed.
>
> There is a delicate situation with cleanup paths assuming that a writable
> mapping must have occurred in circumstances where it may now not have. In
> order to ensure we do not accidentally mark a writable file unwritable by
> mistake, we explicitly track whether we have a writable mapping and
> unmap only if we do.
>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217238
> Signed-off-by: Lorenzo Stoakes <lstoakes(a)gmail.com>
> ---
> mm/mmap.c | 23 ++++++++++++++---------
> 1 file changed, 14 insertions(+), 9 deletions(-)
>
[snip]
Andrew, could you apply the following -fix patch to this? As a bug was
detected in the implementation [0] - I was being over-zealous in setting
the writable_file_mapping flag and had falsely assumed vma->vm_file == file
in all instances of the cleanup. The fix is to only set it in one place.
[0]: https://lore.kernel.org/all/CA+G9fYtL7wK-dE-Tnz4t-GWmQb50EPYa=TWGjpgYU2Z=oe…
----8<----
From 7feea6faada5b10a872c24755cc630220cba619a Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <lstoakes(a)gmail.com>
Date: Mon, 16 Oct 2023 17:17:13 +0100
Subject: [PATCH] mm: perform the mapping_map_writable() check after
call_mmap()
Do not set writable_file_mapping in an instance where it is not appropriate
to do so.
Signed-off-by: Lorenzo Stoakes <lstoakes(a)gmail.com>
---
mm/mmap.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 7f45a08e7973..8b57e42fd980 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2923,10 +2923,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
mm->map_count++;
if (vma->vm_file) {
i_mmap_lock_write(vma->vm_file->f_mapping);
- if (vma_is_shared_maywrite(vma)) {
+ if (vma_is_shared_maywrite(vma))
mapping_allow_writable(vma->vm_file->f_mapping);
- writable_file_mapping = true;
- }
flush_dcache_mmap_lock(vma->vm_file->f_mapping);
vma_interval_tree_insert(vma, &vma->vm_file->f_mapping->i_mmap);
--
2.42.0
Total jobs: 57
Total errors: 11 (19.30%)
LAVA errors: 0 (0.00%)
Test errors: 9 (15.79%)
Job errors: 2 (3.51%)
Infra errors: 0 (0.00%)
Canceled jobs: 0 (0.00%)
Device type: dragonboard-845c
Total jobs: 27
Total errors: 7 (25.93%)
Error type: Test
Error count: 5 (18.52%)
Error: No match for error type 'Test', message 'The network seems not available, as the ping command failed'
Count: 4 (14.81%)
IDs:
db845c-02:
6940788
db845c-07:
6940790
db845c-08:
6938917
db845c-09:
6938924
Error: No match for error type 'Test', message 'lava-docker-test-shell timed out after 596 seconds'
Count: 1 (3.70%)
IDs:
db845c-06:
6938928
Error type: Job
Error count: 2 (7.41%)
Error: wait for prompt timed out
Count: 1 (3.70%)
IDs:
db845c-02:
6940785
Error: No match for error type 'Job', message 'login-action timed out after 870 seconds'
Count: 1 (3.70%)
IDs:
db845c-09:
6938926
Device type: qrb5165-rb5
Total jobs: 26
Total errors: 4 (15.38%)
Error type: Test
Error count: 4 (15.38%)
Error: No match for error type 'Test', message 'The network seems not available, as the ping command failed'
Count: 1 (3.85%)
IDs:
rb5-03:
6939013
Error: No match for error type 'Test', message 'tradefed - adb device lost[74d67c95]'
Count: 3 (11.54%)
IDs:
rb5-03:
6937534 6937536 6937884
Device type: x15
Total jobs: 3
Total errors: 0 (0.00%)
Device type: dragonboard-410c
Total jobs: 1
Total errors: 0 (0.00%)