| Message ID | 20210323212431.15306-1-mwilck@suse.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 077ce028b8e0684d5ee7da573bd835b14b591546 |
| Headers | show |
| Series | [v2,1/2] target: pscsi: avoid OOM in pscsi_map_sg() | expand |
On Tue, Mar 23, 2021 at 10:24:30PM +0100, mwilck@suse.com wrote: > From: Martin Wilck <mwilck@suse.com> > > pscsi_map_sg() uses the variable nr_pages as a hint for bio_kmalloc() > how many vector elements to allocate. If nr_pages is < BIO_MAX_PAGES, > it will be reset to 0 after successful allocation of the bio. > > If bio_add_pc_page() fails later for whatever reason, pscsi_map_sg() > tries to allocate another bio, passing nr_vecs=0. This causes > bio_add_pc_page() to fail immediately in the next call. pci_map_sg() > continues to allocate zero-length bios until memory is exhausted and > the kernel crashes with OOM. This can be easily observed by exporting > a SATA DVD drive via pscsi. The target crashes as soon as the client > tries to access the DVD LUN. In the case I analyzed, bio_add_pc_page() > would fail because the DVD device's max_sectors_kb (128) was > exceeded. > > Avoid this by simply not resetting nr_pages to 0 after allocating the > bio. This way, the client receives an IO error when it tries to send > requests exceeding the devices max_sectors_kb, and eventually gets > it right. The client must still limit max_sectors_kb e.g. by an udev > rule if (like in my case) the driver doesn't report valid block > limits, otherwise it encounters I/O errors. > > Signed-off-by: Martin Wilck <mwilck@suse.com> Looks good, Reviewed-by: Christoph Hellwig <hch@lst.de>
On 3/23/21 2:24 PM, mwilck@suse.com wrote: > From: Martin Wilck <mwilck@suse.com> > > pscsi_map_sg() uses the variable nr_pages as a hint for bio_kmalloc() > how many vector elements to allocate. If nr_pages is < BIO_MAX_PAGES, > it will be reset to 0 after successful allocation of the bio. > > If bio_add_pc_page() fails later for whatever reason, pscsi_map_sg() > tries to allocate another bio, passing nr_vecs=0. This causes > bio_add_pc_page() to fail immediately in the next call. pci_map_sg() > continues to allocate zero-length bios until memory is exhausted and > the kernel crashes with OOM. This can be easily observed by exporting > a SATA DVD drive via pscsi. The target crashes as soon as the client > tries to access the DVD LUN. In the case I analyzed, bio_add_pc_page() > would fail because the DVD device's max_sectors_kb (128) was > exceeded. > > Avoid this by simply not resetting nr_pages to 0 after allocating the > bio. This way, the client receives an IO error when it tries to send > requests exceeding the devices max_sectors_kb, and eventually gets > it right. The client must still limit max_sectors_kb e.g. by an udev > rule if (like in my case) the driver doesn't report valid block > limits, otherwise it encounters I/O errors. > > Signed-off-by: Martin Wilck <mwilck@suse.com> > --- > drivers/target/target_core_pscsi.c | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c > index 7b1035e..977362d 100644 > --- a/drivers/target/target_core_pscsi.c > +++ b/drivers/target/target_core_pscsi.c > @@ -881,7 +881,6 @@ pscsi_map_sg(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents, > if (!bio) { > new_bio: > nr_vecs = bio_max_segs(nr_pages); > - nr_pages -= nr_vecs; > /* > * Calls bio_kmalloc() and sets bio->bi_end_io() > */ > Reviewed-by: Lee Duncan <lduncan@suse.com>
On Tue, 23 Mar 2021 22:24:30 +0100, mwilck@suse.com wrote: > pscsi_map_sg() uses the variable nr_pages as a hint for bio_kmalloc() > how many vector elements to allocate. If nr_pages is < BIO_MAX_PAGES, > it will be reset to 0 after successful allocation of the bio. > > If bio_add_pc_page() fails later for whatever reason, pscsi_map_sg() > tries to allocate another bio, passing nr_vecs=0. This causes > bio_add_pc_page() to fail immediately in the next call. pci_map_sg() > continues to allocate zero-length bios until memory is exhausted and > the kernel crashes with OOM. This can be easily observed by exporting > a SATA DVD drive via pscsi. The target crashes as soon as the client > tries to access the DVD LUN. In the case I analyzed, bio_add_pc_page() > would fail because the DVD device's max_sectors_kb (128) was > exceeded. > > [...] Applied to 5.12/scsi-fixes, thanks! [1/2] target: pscsi: avoid OOM in pscsi_map_sg() https://git.kernel.org/mkp/scsi/c/077ce028b8e0 [2/2] target: pscsi: cleanup after failure in pscsi_map_sg() https://git.kernel.org/mkp/scsi/c/36fa766faa0c
diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c index 7b1035e..977362d 100644 --- a/drivers/target/target_core_pscsi.c +++ b/drivers/target/target_core_pscsi.c @@ -881,7 +881,6 @@ pscsi_map_sg(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents, if (!bio) { new_bio: nr_vecs = bio_max_segs(nr_pages); - nr_pages -= nr_vecs; /* * Calls bio_kmalloc() and sets bio->bi_end_io() */