Messages in this thread | | | Date | Tue, 19 Dec 2023 09:51:12 +0800 | Subject | Re: [PATCH 1/4] ext4: fix double-free of blocks due to wrong extents moved_len | From | Baokun Li <> |
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On 2023/12/18 23:32, Jan Kara wrote: > On Mon 18-12-23 22:18:11, Baokun Li wrote: >> In ext4_move_extents(), moved_len is only updated when all moves are >> successfully executed, and only discards orig_inode and donor_inode >> preallocations when moved_len is not zero. When the loop fails to exit >> after successfully moving some extents, moved_len is not updated and >> remains at 0, so it does not discard the preallocations. >> >> If the moved extents overlap with the preallocated extents, the >> overlapped extents are freed twice in ext4_mb_release_inode_pa() and >> ext4_process_freed_data() (as described in commit 94d7c16cbbbd), and >> bb_free is incremented twice. Hence when trim is executed, a zero-division >> bug is triggered in mb_update_avg_fragment_size() because bb_free is not >> zero and bb_fragments is zero. >> >> Therefore, update move_len after each extent move to avoid the issue. >> >> Reported-by: Wei Chen <harperchen1110@gmail.com> >> Reported-by: xingwei lee <xrivendell7@gmail.com> >> Closes: https://lore.kernel.org/r/CAO4mrferzqBUnCag8R3m2zf897ts9UEuhjFQGPtODT92rYyR2Q@mail.gmail.com >> Fixes: fcf6b1b729bc ("ext4: refactor ext4_move_extents code base") >> CC: stable@vger.kernel.org # 3.18 >> Signed-off-by: Baokun Li <libaokun1@huawei.com> >> --- >> fs/ext4/move_extent.c | 3 +-- >> 1 file changed, 1 insertion(+), 2 deletions(-) >> >> diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c >> index 3aa57376d9c2..4b9b503c6346 100644 >> --- a/fs/ext4/move_extent.c >> +++ b/fs/ext4/move_extent.c >> @@ -672,7 +672,7 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk, >> */ >> ext4_double_up_write_data_sem(orig_inode, donor_inode); >> /* Swap original branches with new branches */ >> - move_extent_per_page(o_filp, donor_inode, >> + *moved_len += move_extent_per_page(o_filp, donor_inode, >> orig_page_index, donor_page_index, >> offset_in_page, cur_len, >> unwritten, &ret); > Although this is currently fine, I think ext4_move_extents() should be > careful and zero out *moved_len before it starts using it. Totally agree, now __ext4_ioctl zeroes it out, but to avoid code logic changes or new callers afterward, I'll zero it out before using it in ext4_move_extents() in the next version. > >> @@ -682,7 +682,6 @@ ext4_move_extents(struct file *o_filp, struct file *d_filp, __u64 orig_blk, >> o_start += cur_len; >> d_start += cur_len; >> } >> - *moved_len = o_start - orig_blk; >> if (*moved_len > len) >> *moved_len = len; > So I'm not sure the *moved_len > len condition can ever trigger but if it > does, we'd need to check it whenever we are returning moved_len. So either > I'd delete the condition or move it to the out label. > > Honza As the code stands now, the *moved_len > len condition never occurs, and is supposed to be code left over from the refactoring in [Fixes], which I'll remove in the next version.
Thank you for your review! -- With Best Regards, Baokun Li .
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