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Liam R. Howlett
64c37e134b
If a memory allocation fails during dup_mmap(), the maple tree can be left in an unsafe state for other iterators besides the exit path. All the locks are dropped before the exit_mmap() call (in mm/mmap.c), but the incomplete mm_struct can be reached through (at least) the rmap finding the vmas which have a pointer back to the mm_struct. Up to this point, there have been no issues with being able to find an mm_struct that was only partially initialised. Syzbot was able to make the incomplete mm_struct fail with recent forking changes, so it has been proven unsafe to use the mm_struct that hasn't been initialised, as referenced in the link below. Although8ac662f5da("fork: avoid inappropriate uprobe access to invalid mm") fixed the uprobe access, it does not completely remove the race. This patch sets the MMF_OOM_SKIP to avoid the iteration of the vmas on the oom side (even though this is extremely unlikely to be selected as an oom victim in the race window), and sets MMF_UNSTABLE to avoid other potential users from using a partially initialised mm_struct. When registering vmas for uprobe, skip the vmas in an mm that is marked unstable. Modifying a vma in an unstable mm may cause issues if the mm isn't fully initialised. Link: https://lore.kernel.org/all/[email protected]/ Link: https://lkml.kernel.org/r/[email protected] Fixes:d240629148("fork: use __mt_dup() to duplicate maple tree in dup_mmap()") Signed-off-by: Liam R. Howlett <[email protected]> Reviewed-by: Lorenzo Stoakes <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: Masami Hiramatsu <[email protected]> Cc: Jann Horn <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Peng Zhang <[email protected]> Cc: Matthew Wilcox <[email protected]> Signed-off-by: Andrew Morton <[email protected]>