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nbd: use shifts rather than multiplies

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commit fad7cd3310 ("nbd: add the check to prevent overflow in
__nbd_ioctl()") raised an issue from the fallback helpers added in
commit f0907827a8 ("compiler.h: enable builtin overflow checkers and
add fallback code")

ERROR: modpost: "__divdi3" [drivers/block/nbd.ko] undefined!

As Stephen Rothwell notes:
  The added check_mul_overflow() call is being passed 64 bit values.
  COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW is not set for this build (see
  include/linux/overflow.h).

Specifically, the helpers for checking whether the results of a
multiplication overflowed (__unsigned_mul_overflow,
__signed_add_overflow) use the division operator when
!COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW.  This is problematic for 64b
operands on 32b hosts.

This was fixed upstream by
commit 76ae847497 ("Documentation: raise minimum supported version of
GCC to 5.1")
which is not suitable to be backported to stable.

Further, __builtin_mul_overflow() would emit a libcall to a
compiler-rt-only symbol when compiling with clang < 14 for 32b targets.

ld.lld: error: undefined symbol: __mulodi4

In order to keep stable buildable with GCC 4.9 and clang < 14, modify
struct nbd_config to instead track the number of bits of the block size;
reconstructing the block size using runtime checked shifts that are not
problematic for those compilers and in a ways that can be backported to
stable.

In nbd_set_size, we do validate that the value of blksize must be a
power of two (POT) and is in the range of [512, PAGE_SIZE] (both
inclusive).

This does modify the debugfs interface.

Cc: stable@vger.kernel.org
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Link: https://github.com/ClangBuiltLinux/linux/issues/1438
Link: https://lore.kernel.org/all/20210909182525.372ee687@canb.auug.org.au/
Link: https://lore.kernel.org/stable/CAHk-=whiQBofgis_rkniz8GBP9wZtSZdcDEffgSLO62BUGV3gg@mail.gmail.com/
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: Nathan Chancellor <nathan@kernel.org>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Suggested-by: Kees Cook <keescook@chromium.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20210920232533.4092046-1-ndesaulniers@google.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Nick Desaulniers 2021-09-20 16:25:33 -07:00 committed by Jens Axboe
parent ebc69e897e
commit 41e76c6a3c
1 changed files with 17 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
drivers/block/nbd.c
View File

@ -97,13 +97,18 @@ struct nbd_config {
atomic_t recv_threads;
wait_queue_head_t recv_wq;
loff_t blksize;
unsigned int blksize_bits;
loff_t bytesize;
#if IS_ENABLED(CONFIG_DEBUG_FS)
struct dentry *dbg_dir;
#endif
};
static inline unsigned int nbd_blksize(struct nbd_config *config)
{
return 1u << config->blksize_bits;
}
struct nbd_device {
struct blk_mq_tag_set tag_set;
@ -146,7 +151,7 @@ static struct dentry *nbd_dbg_dir;
#define NBD_MAGIC 0x68797548
#define NBD_DEF_BLKSIZE 1024
#define NBD_DEF_BLKSIZE_BITS 10
static unsigned int nbds_max = 16;
static int max_part = 16;
@ -317,12 +322,12 @@ static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize,
loff_t blksize)
{
if (!blksize)
blksize = NBD_DEF_BLKSIZE;
blksize = 1u << NBD_DEF_BLKSIZE_BITS;
if (blksize < 512 || blksize > PAGE_SIZE || !is_power_of_2(blksize))
return -EINVAL;
nbd->config->bytesize = bytesize;
nbd->config->blksize = blksize;
nbd->config->blksize_bits = __ffs(blksize);
if (!nbd->task_recv)
return 0;
@ -1337,7 +1342,7 @@ static int nbd_start_device(struct nbd_device *nbd)
args->index = i;
queue_work(nbd->recv_workq, &args->work);
}
return nbd_set_size(nbd, config->bytesize, config->blksize);
return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
}
static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *bdev)
@ -1406,11 +1411,11 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
case NBD_SET_BLKSIZE:
return nbd_set_size(nbd, config->bytesize, arg);
case NBD_SET_SIZE:
return nbd_set_size(nbd, arg, config->blksize);
return nbd_set_size(nbd, arg, nbd_blksize(config));
case NBD_SET_SIZE_BLOCKS:
if (check_mul_overflow((loff_t)arg, config->blksize, &bytesize))
if (check_shl_overflow(arg, config->blksize_bits, &bytesize))
return -EINVAL;
return nbd_set_size(nbd, bytesize, config->blksize);
return nbd_set_size(nbd, bytesize, nbd_blksize(config));
case NBD_SET_TIMEOUT:
nbd_set_cmd_timeout(nbd, arg);
return 0;
@ -1476,7 +1481,7 @@ static struct nbd_config *nbd_alloc_config(void)
atomic_set(&config->recv_threads, 0);
init_waitqueue_head(&config->recv_wq);
init_waitqueue_head(&config->conn_wait);
config->blksize = NBD_DEF_BLKSIZE;
config->blksize_bits = NBD_DEF_BLKSIZE_BITS;
atomic_set(&config->live_connections, 0);
try_module_get(THIS_MODULE);
return config;
@ -1604,7 +1609,7 @@ static int nbd_dev_dbg_init(struct nbd_device *nbd)
debugfs_create_file("tasks", 0444, dir, nbd, &nbd_dbg_tasks_fops);
debugfs_create_u64("size_bytes", 0444, dir, &config->bytesize);
debugfs_create_u32("timeout", 0444, dir, &nbd->tag_set.timeout);
debugfs_create_u64("blocksize", 0444, dir, &config->blksize);
debugfs_create_u32("blocksize_bits", 0444, dir, &config->blksize_bits);
debugfs_create_file("flags", 0444, dir, nbd, &nbd_dbg_flags_fops);
return 0;
@ -1826,7 +1831,7 @@ nbd_device_policy[NBD_DEVICE_ATTR_MAX + 1] = {
static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
{
struct nbd_config *config = nbd->config;
u64 bsize = config->blksize;
u64 bsize = nbd_blksize(config);
u64 bytes = config->bytesize;
if (info->attrs[NBD_ATTR_SIZE_BYTES])
@ -1835,7 +1840,7 @@ static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
if (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES])
bsize = nla_get_u64(info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]);
if (bytes != config->bytesize || bsize != config->blksize)
if (bytes != config->bytesize || bsize != nbd_blksize(config))
return nbd_set_size(nbd, bytes, bsize);
return 0;
}