On 11/19/24 18:59, Liam R. Howlett wrote: > From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx> > > The mmap_region() function tries to install a new vma, which requires a > pre-allocation for the maple tree write due to the complex locking > scenarios involved. > > Recent efforts to simplify the error recovery required the relocation of > the preallocation of the maple tree nodes (via vma_iter_prealloc() > calling mas_preallocate()) higher in the function. > > The relocation of the preallocation meant that, if there was a file > associated with the vma and the driver call (mmap_file()) modified the > vma flags, then a new merge of the new vma with existing vmas is > attempted. > > During the attempt to merge the existing vma with the new vma, the vma > iterator is used - the same iterator that would be used for the next > write attempt to the tree. In the event of needing a further allocation > and if the new allocations fails, the vma iterator (and contained maple > state) will cleaned up, including freeing all previous allocations and > will be reset internally. > > Upon returning to the __mmap_region() function, the error is available > in the vma_merge_struct and can be used to detect the -ENOMEM status. > > Hitting an -ENOMEM scenario after the driver callback leaves the system > in a state that undoing the mapping is worse than continuing by dipping > into the reserve. > > A preallocation should be performed in the case of an -ENOMEM and the > allocations were lost during the failure scenario. The __GFP_NOFAIL > flag is used in the allocation to ensure the allocation succeeds after > implicitly telling the driver that the mapping was happening. > > The range is already set in the vma_iter_store() call below, so it is > not necessary and is dropped. > > Reported-by: syzbot+bc6bfc25a68b7a020ee1@xxxxxxxxxxxxxxxxxxxxxxxxx > Closes: https://syzkaller.appspot.com/x/log.txt?x=17b0ace8580000 > Fixes: 5de195060b2e2 ("mm: resolve faulty mmap_region() error path behaviour") > Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> > Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> > Cc: Vlastimil Babka <vbabka@xxxxxxx> > Cc: Jann Horn <jannh@xxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
