[PATCH v2 1/2] target: pscsi: avoid OOM in pscsi_map_sg()

[PATCH v2 1/2] target: pscsi: avoid OOM in pscsi_map_sg()

[mwilck]

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()
 				 */
-- 
2.26.2

[PATCH v2 2/2] target: pscsi: cleanup after failure in pscsi_map_sg()

[mwilck]

From: Martin Wilck <mwilck@suse.com>

If pscsi_map_sg() fails, make sure to drop references to already
allocated bios.

Signed-off-by: Martin Wilck <mwilck@suse.com>
---
 drivers/target/target_core_pscsi.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
index 977362d..1c9aeab 100644
--- a/drivers/target/target_core_pscsi.c
+++ b/drivers/target/target_core_pscsi.c
@@ -937,6 +937,14 @@ pscsi_map_sg(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
 
 	return 0;
 fail:
+	if (bio)
+		bio_put(bio);
+	while (req->bio) {
+		bio = req->bio;
+		req->bio = bio->bi_next;
+		bio_put(bio);
+	}
+	req->biotail = NULL;
 	return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
 }
 
-- 
2.26.2

Re: [PATCH v2 1/2] target: pscsi: avoid OOM in pscsi_map_sg()

[Christoph Hellwig]

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>

Re: [PATCH v2 2/2] target: pscsi: cleanup after failure in pscsi_map_sg()

[Christoph Hellwig]

On Tue, Mar 23, 2021 at 10:24:31PM +0100, mwilck@suse.com wrote:
> From: Martin Wilck <mwilck@suse.com>
> 
> If pscsi_map_sg() fails, make sure to drop references to already
> allocated bios.
> 
> Signed-off-by: Martin Wilck <mwilck@suse.com>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v2 1/2] target: pscsi: avoid OOM in pscsi_map_sg()

[Lee Duncan]

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>

Re: [PATCH v2 2/2] target: pscsi: cleanup after failure in pscsi_map_sg()

[Lee Duncan]

On 3/23/21 2:24 PM, mwilck@suse.com wrote:
> From: Martin Wilck <mwilck@suse.com>
> 
> If pscsi_map_sg() fails, make sure to drop references to already
> allocated bios.
> 
> Signed-off-by: Martin Wilck <mwilck@suse.com>
> ---
>  drivers/target/target_core_pscsi.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
> index 977362d..1c9aeab 100644
> --- a/drivers/target/target_core_pscsi.c
> +++ b/drivers/target/target_core_pscsi.c
> @@ -937,6 +937,14 @@ pscsi_map_sg(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
>  
>  	return 0;
>  fail:
> +	if (bio)
> +		bio_put(bio);
> +	while (req->bio) {
> +		bio = req->bio;
> +		req->bio = bio->bi_next;
> +		bio_put(bio);
> +	}
> +	req->biotail = NULL;
>  	return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
>  }
>  
> 

Reviewed-by: Lee Duncan <lduncan@suse.com>

Re: [PATCH v2 1/2] target: pscsi: avoid OOM in pscsi_map_sg()

[Martin K. Petersen]

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

-- 
Martin K. Petersen	Oracle Linux Engineering