[PATCH v3][next] scsi: aacraid: Replace one-element array with flexible-array member

Gustavo A. R. Silva
2021-04-21T18:55:53Z

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Refactor the code according to the use of a flexible-array member in
struct aac_raw_io2 instead of one-element array, and use the
struct_size() helper.

Also, this helps with the ongoing efforts to enable -Warray-bounds by
fixing the following warnings:

drivers/scsi/aacraid/aachba.c: In function ‘aac_build_sgraw2’:
drivers/scsi/aacraid/aachba.c:3970:18: warning: array subscript 1 is above array bounds of ‘struct sge_ieee1212[1]’ [-Warray-bounds]
3970 | if (rio2->sge[j].length % (i*PAGE_SIZE)) {
| ~~~~~~~~~^~~
drivers/scsi/aacraid/aachba.c:3974:27: warning: array subscript 1 is above array bounds of ‘struct sge_ieee1212[1]’ [-Warray-bounds]
3974 | nseg_new += (rio2->sge[j].length / (i*PAGE_SIZE));
| ~~~~~~~~~^~~
drivers/scsi/aacraid/aachba.c:4011:28: warning: array subscript 1 is above array bounds of ‘struct sge_ieee1212[1]’ [-Warray-bounds]
4011 | for (j = 0; j < rio2->sge[i].length / (pages * PAGE_SIZE); ++j) {
| ~~~~~~~~~^~~
drivers/scsi/aacraid/aachba.c:4012:24: warning: array subscript 1 is above array bounds of ‘struct sge_ieee1212[1]’ [-Warray-bounds]
4012 | addr_low = rio2->sge[i].addrLow + j * pages * PAGE_SIZE;
| ~~~~~~~~~^~~
drivers/scsi/aacraid/aachba.c:4014:33: warning: array subscript 1 is above array bounds of ‘struct sge_ieee1212[1]’ [-Warray-bounds]
4014 | sge[pos].addrHigh = rio2->sge[i].addrHigh;
| ~~~~~~~~~^~~
drivers/scsi/aacraid/aachba.c:4015:28: warning: array subscript 1 is above array bounds of ‘struct sge_ieee1212[1]’ [-Warray-bounds]
4015 | if (addr_low < rio2->sge[i].addrLow)
| ~~~~~~~~~^~~

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Build-tested-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/60414244.ur4%2FkI+fBF1ohKZs%25lkp@intel.com/
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
Changes in v3:
- Use (nseg_new-1)*sizeof(struct sge_ieee1212) to calculate
size in call to memcpy() in order to avoid any confusion.

Changes in v2:
- Add code comment for clarification.

drivers/scsi/aacraid/aachba.c | 10 +++++-----
drivers/scsi/aacraid/aacraid.h | 2 +-
2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/scsi/aacraid/aachba.c b/drivers/scsi/aacraid/aachba.c
index f1f62b5da8b7..46b8dffce2dd 100644
--- a/drivers/scsi/aacraid/aachba.c
+++ b/drivers/scsi/aacraid/aachba.c
@@ -1235,8 +1235,8 @@ static int aac_read_raw_io(struct fib * fib, struct scsi_cmnd * cmd, u64 lba, u3
if (ret < 0)
return ret;
command = ContainerRawIo2;
- fibsize = sizeof(struct aac_raw_io2) +
- ((le32_to_cpu(readcmd2->sgeCnt)-1) * sizeof(struct sge_ieee1212));
+ fibsize = struct_size(readcmd2, sge,
+ le32_to_cpu(readcmd2->sgeCnt));
} else {
struct aac_raw_io *readcmd;
readcmd = (struct aac_raw_io *) fib_data(fib);
@@ -1366,8 +1366,8 @@ static int aac_write_raw_io(struct fib * fib, struct scsi_cmnd * cmd, u64 lba, u
if (ret < 0)
return ret;
command = ContainerRawIo2;
- fibsize = sizeof(struct aac_raw_io2) +
- ((le32_to_cpu(writecmd2->sgeCnt)-1) * sizeof(struct sge_ieee1212));
+ fibsize = struct_size(writecmd2, sge,
+ le32_to_cpu(writecmd2->sgeCnt));
} else {
struct aac_raw_io *writecmd;
writecmd = (struct aac_raw_io *) fib_data(fib);
@@ -3998,7 +3998,7 @@ static int aac_convert_sgraw2(struct aac_raw_io2 *rio2, int pages, int nseg, int
if (aac_convert_sgl == 0)
return 0;

- sge = kmalloc_array(nseg_new, sizeof(struct sge_ieee1212), GFP_ATOMIC);
+ sge = kmalloc_array(nseg_new, sizeof(*sge), GFP_ATOMIC);
if (sge == NULL)
return -ENOMEM;

diff --git a/drivers/scsi/aacraid/aacraid.h b/drivers/scsi/aacraid/aacraid.h
index e3e4ecbea726..3733df77bc65 100644
--- a/drivers/scsi/aacraid/aacraid.h
+++ b/drivers/scsi/aacraid/aacraid.h
@@ -1929,7 +1929,7 @@ struct aac_raw_io2 {
u8 bpComplete; /* reserved for F/W use */
u8 sgeFirstIndex; /* reserved for F/W use */
u8 unused[4];
- struct sge_ieee1212 sge[1];
+ struct sge_ieee1212 sge[];
};

#define CT_FLUSH_CACHE 129
--
2.27.0