Hi Jann, > Subject: [PATCH 1/3] udmabuf: fix racy memfd sealing check > > The current check_memfd_seals() is racy: Since we first do > check_memfd_seals() and then udmabuf_pin_folios() without holding any > relevant lock across both, F_SEAL_WRITE can be set in between. > This is problematic because we can end up holding pins to pages in a > write-sealed memfd. > > Fix it using the inode lock, that's probably the easiest way. > In the future, we might want to consider moving this logic into memfd, > especially if anyone else wants to use memfd_pin_folios(). > > Reported-by: Julian Orth <ju.orth@xxxxxxxxx> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219106 > Closes: > https://lore.kernel.org/r/CAG48ez0w8HrFEZtJkfmkVKFDhE5aP7nz=obrimeTg > pD+StkV9w@xxxxxxxxxxxxxx > Fixes: fbb0de795078 ("Add udmabuf misc device") > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Jann Horn <jannh@xxxxxxxxxx> > --- > drivers/dma-buf/udmabuf.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c > index > 8ce1f074c2d32a0a9f59ff7184359e37d56548c6..662b9a26e06668bf59ab36d0 > 7c0648c7b02ee5ae 100644 > --- a/drivers/dma-buf/udmabuf.c > +++ b/drivers/dma-buf/udmabuf.c > @@ -436,14 +436,15 @@ static long udmabuf_create(struct miscdevice > *device, > goto err; > } > > + inode_lock_shared(memfd->f_inode); I think having inode_lock_shared(file_inode(memfd)) looks a bit more cleaner. Also, wouldn't it be more appropriate here to take the writer's lock instead of the reader's lock given what we are doing (pinning) in udmabuf_create()? Thanks, Vivek > ret = check_memfd_seals(memfd); > - if (ret < 0) { > - fput(memfd); > - goto err; > - } > + if (ret) > + goto out_unlock; > > ret = udmabuf_pin_folios(ubuf, memfd, list[i].offset, > list[i].size, folios); > +out_unlock: > + inode_unlock_shared(memfd->f_inode); > fput(memfd); > if (ret) > goto err; > > -- > 2.47.0.338.g60cca15819-goog
