[PATCH AUTOSEL 6.2 01/18] RDMA/core: Fix multiple -Warray-bounds warnings

Sasha Levin
2023-05-09T21:21:13Z

From: "Gustavo A. R. Silva" <gustavoars@kernel.org>

[ Upstream commit aa4d540b4150052ae3b36d286b9c833a961ce291 ]

GCC-13 (and Clang)[1] does not like to access a partially allocated
object, since it cannot reason about it for bounds checking.

In this case 140 bytes are allocated for an object of type struct
ib_umad_packet:

packet = kzalloc(sizeof(*packet) + IB_MGMT_RMPP_HDR, GFP_KERNEL);

However, notice that sizeof(*packet) is only 104 bytes:

struct ib_umad_packet {
struct ib_mad_send_buf * msg; /* 0 8 */
struct ib_mad_recv_wc * recv_wc; /* 8 8 */
struct list_head list; /* 16 16 */
int length; /* 32 4 */

/* XXX 4 bytes hole, try to pack */

struct ib_user_mad mad __attribute__((__aligned__(8))); /* 40 64 */

/* size: 104, cachelines: 2, members: 5 */
/* sum members: 100, holes: 1, sum holes: 4 */
/* forced alignments: 1, forced holes: 1, sum forced holes: 4 */
/* last cacheline: 40 bytes */
} __attribute__((__aligned__(8)));

and 36 bytes extra bytes are allocated for a flexible-array member in
struct ib_user_mad:

include/rdma/ib_mad.h:
120 enum {
...
123 IB_MGMT_RMPP_HDR = 36,
... }

struct ib_user_mad {
struct ib_user_mad_hdr hdr; /* 0 64 */
/* --- cacheline 1 boundary (64 bytes) --- */
__u64 data[] __attribute__((__aligned__(8))); /* 64 0 */

/* size: 64, cachelines: 1, members: 2 */
/* forced alignments: 1 */
} __attribute__((__aligned__(8)));

So we have sizeof(*packet) + IB_MGMT_RMPP_HDR == 140 bytes

Then the address of the flex-array member (for which only 36 bytes were
allocated) is casted and copied into a pointer to struct ib_rmpp_mad,
which, in turn, is of size 256 bytes:

rmpp_mad = (struct ib_rmpp_mad *) packet->mad.data;

struct ib_rmpp_mad {
struct ib_mad_hdr mad_hdr; /* 0 24 */
struct ib_rmpp_hdr rmpp_hdr; /* 24 12 */
u8 data[220]; /* 36 220 */

/* size: 256, cachelines: 4, members: 3 */
};

The thing is that those 36 bytes allocated for flex-array member data
in struct ib_user_mad onlly account for the size of both struct ib_mad_hdr
and struct ib_rmpp_hdr, but nothing is left for array u8 data[220].
So, the compiler is legitimately complaining about accessing an object
for which not enough memory was allocated.

Apparently, the only members of struct ib_rmpp_mad that are relevant
(that are actually being used) in function ib_umad_write() are mad_hdr
and rmpp_hdr. So, instead of casting packet->mad.data to
(struct ib_rmpp_mad *) create a new structure

struct ib_rmpp_mad_hdr {
struct ib_mad_hdr mad_hdr;
struct ib_rmpp_hdr rmpp_hdr;
} __packed;

and cast packet->mad.data to (struct ib_rmpp_mad_hdr *).

Notice that

IB_MGMT_RMPP_HDR == sizeof(struct ib_rmpp_mad_hdr) == 36 bytes

Refactor the rest of the code, accordingly.

Fix the following warnings seen under GCC-13 and -Warray-bounds:
drivers/infiniband/core/user_mad.c:564:50: warning: array subscript ‘struct ib_rmpp_mad[0]’ is partly outside array bounds of ‘unsigned char[140]’ [-Warray-bounds=]
drivers/infiniband/core/user_mad.c:566:42: warning: array subscript ‘struct ib_rmpp_mad[0]’ is partly outside array bounds of ‘unsigned char[140]’ [-Warray-bounds=]
drivers/infiniband/core/user_mad.c:618:25: warning: array subscript ‘struct ib_rmpp_mad[0]’ is partly outside array bounds of ‘unsigned char[140]’ [-Warray-bounds=]
drivers/infiniband/core/user_mad.c:622:44: warning: array subscript ‘struct ib_rmpp_mad[0]’ is partly outside array bounds of ‘unsigned char[140]’ [-Warray-bounds=]

Link: https://github.com/KSPP/linux/issues/273
Link: https://godbolt.org/z/oYWaGM4Yb [1]
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/ZBpB91qQcB10m3Fw@work
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/infiniband/core/user_mad.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/infiniband/core/user_mad.c b/drivers/infiniband/core/user_mad.c
index f83954180a338..d21c0a042f0a5 100644
--- a/drivers/infiniband/core/user_mad.c
+++ b/drivers/infiniband/core/user_mad.c
@@ -131,6 +131,11 @@ struct ib_umad_packet {
struct ib_user_mad mad;
};

+struct ib_rmpp_mad_hdr {
+ struct ib_mad_hdr mad_hdr;
+ struct ib_rmpp_hdr rmpp_hdr;
+} __packed;
+
#define CREATE_TRACE_POINTS
#include <trace/events/ib_umad.h>

@@ -494,11 +499,11 @@ static ssize_t ib_umad_write(struct file *filp, const char __user *buf,
size_t count, loff_t *pos)
{
struct ib_umad_file *file = filp->private_data;
+ struct ib_rmpp_mad_hdr *rmpp_mad_hdr;
struct ib_umad_packet *packet;
struct ib_mad_agent *agent;
struct rdma_ah_attr ah_attr;
struct ib_ah *ah;
- struct ib_rmpp_mad *rmpp_mad;
__be64 *tid;
int ret, data_len, hdr_len, copy_offset, rmpp_active;
u8 base_version;
@@ -506,7 +511,7 @@ static ssize_t ib_umad_write(struct file *filp, const char __user *buf,
if (count < hdr_size(file) + IB_MGMT_RMPP_HDR)
return -EINVAL;

- packet = kzalloc(sizeof *packet + IB_MGMT_RMPP_HDR, GFP_KERNEL);
+ packet = kzalloc(sizeof(*packet) + IB_MGMT_RMPP_HDR, GFP_KERNEL);
if (!packet)
return -ENOMEM;

@@ -560,13 +565,13 @@ static ssize_t ib_umad_write(struct file *filp, const char __user *buf,
goto err_up;
}

- rmpp_mad = (struct ib_rmpp_mad *) packet->mad.data;
- hdr_len = ib_get_mad_data_offset(rmpp_mad->mad_hdr.mgmt_class);
+ rmpp_mad_hdr = (struct ib_rmpp_mad_hdr *)packet->mad.data;
+ hdr_len = ib_get_mad_data_offset(rmpp_mad_hdr->mad_hdr.mgmt_class);

- if (ib_is_mad_class_rmpp(rmpp_mad->mad_hdr.mgmt_class)
+ if (ib_is_mad_class_rmpp(rmpp_mad_hdr->mad_hdr.mgmt_class)
&& ib_mad_kernel_rmpp_agent(agent)) {
copy_offset = IB_MGMT_RMPP_HDR;
- rmpp_active = ib_get_rmpp_flags(&rmpp_mad->rmpp_hdr) &
+ rmpp_active = ib_get_rmpp_flags(&rmpp_mad_hdr->rmpp_hdr) &
IB_MGMT_RMPP_FLAG_ACTIVE;
} else {
copy_offset = IB_MGMT_MAD_HDR;
@@ -615,12 +620,12 @@ static ssize_t ib_umad_write(struct file *filp, const char __user *buf,
tid = &((struct ib_mad_hdr *) packet->msg->mad)->tid;
*tid = cpu_to_be64(((u64) agent->hi_tid) << 32 |
(be64_to_cpup(tid) & 0xffffffff));
- rmpp_mad->mad_hdr.tid = *tid;
+ rmpp_mad_hdr->mad_hdr.tid = *tid;
}

if (!ib_mad_kernel_rmpp_agent(agent)
- && ib_is_mad_class_rmpp(rmpp_mad->mad_hdr.mgmt_class)
- && (ib_get_rmpp_flags(&rmpp_mad->rmpp_hdr) & IB_MGMT_RMPP_FLAG_ACTIVE)) {
+ && ib_is_mad_class_rmpp(rmpp_mad_hdr->mad_hdr.mgmt_class)
+ && (ib_get_rmpp_flags(&rmpp_mad_hdr->rmpp_hdr) & IB_MGMT_RMPP_FLAG_ACTIVE)) {
spin_lock_irq(&file->send_lock);
list_add_tail(&packet->list, &file->send_list);
spin_unlock_irq(&file->send_lock);
--
2.39.2