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mm/hugetlb.c: fix UAF of vma in hugetlb fault pathway

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Syzbot reports a UAF in hugetlb_fault().  This happens because
vmf_anon_prepare() could drop the per-VMA lock and allow the current VMA
to be freed before hugetlb_vma_unlock_read() is called.

We can fix this by using a modified version of vmf_anon_prepare() that
doesn't release the VMA lock on failure, and then release it ourselves
after hugetlb_vma_unlock_read().

Link: https://lkml.kernel.org/r/20240914194243.245-2-vishal.moola@gmail.com
Fixes: 9acad7ba3e ("hugetlb: use vmf_anon_prepare() instead of anon_vma_prepare()")
Reported-by: syzbot+2dab93857ee95f2eeb08@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-mm/00000000000067c20b06219fbc26@google.com/
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Vishal Moola (Oracle) 2024-09-14 12:41:19 -07:00 committed by Andrew Morton
parent 2a058ab328
commit 98b74bb4d7
1 changed files with 18 additions and 2 deletions
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20
mm/hugetlb.c
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@ -6048,7 +6048,7 @@ retry_avoidcopy:
* When the original hugepage is shared one, it does not have
* anon_vma prepared.
*/
ret = vmf_anon_prepare(vmf);
ret = __vmf_anon_prepare(vmf);
if (unlikely(ret))
goto out_release_all;
@ -6247,7 +6247,7 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping,
}
if (!(vma->vm_flags & VM_MAYSHARE)) {
ret = vmf_anon_prepare(vmf);
ret = __vmf_anon_prepare(vmf);
if (unlikely(ret))
goto out;
}
@ -6378,6 +6378,14 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping,
folio_unlock(folio);
out:
hugetlb_vma_unlock_read(vma);
/*
* We must check to release the per-VMA lock. __vmf_anon_prepare() is
* the only way ret can be set to VM_FAULT_RETRY.
*/
if (unlikely(ret & VM_FAULT_RETRY))
vma_end_read(vma);
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
return ret;
@ -6599,6 +6607,14 @@ out_ptl:
}
out_mutex:
hugetlb_vma_unlock_read(vma);
/*
* We must check to release the per-VMA lock. __vmf_anon_prepare() in
* hugetlb_wp() is the only way ret can be set to VM_FAULT_RETRY.
*/
if (unlikely(ret & VM_FAULT_RETRY))
vma_end_read(vma);
mutex_unlock(&hugetlb_fault_mutex_table[hash]);
/*
* Generally it's safe to hold refcount during waiting page lock. But