[PATCH 28/44] drivers/usb/storage: use min() instead of min_t()

[david.lai...@gmail.com]

From: David Laight <david.lai...@gmail.com>

min_t(unsigned int, a, b) casts an 'unsigned long' to 'unsigned int'.
Use min(a, b) instead as it promotes any 'unsigned int' to 'unsigned long'
and so cannot discard significant bits.

In this case the 'unsigned long' value is small enough that the result
is ok.

Detected by an extra check added to min_t().

Signed-off-by: David Laight <david.lai...@gmail.com>
---
drivers/usb/storage/protocol.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/usb/storage/protocol.c b/drivers/usb/storage/protocol.c
index 9033e505db7f..0cff54ad90fa 100644
--- a/drivers/usb/storage/protocol.c
+++ b/drivers/usb/storage/protocol.c
@@ -139,8 +139,7 @@ unsigned int usb_stor_access_xfer_buf(unsigned char *buffer,
return cnt;

while (sg_miter_next(&miter) && cnt < buflen) {
- unsigned int len = min_t(unsigned int, miter.length,
- buflen - cnt);
+ unsigned int len = min(miter.length, buflen - cnt);

if (dir == FROM_XFER_BUF)
memcpy(buffer + cnt, miter.addr, len);
--
2.39.5

[david.lai...@gmail.com]

From: David Laight <david.lai...@gmail.com>

It in not uncommon for code to use min_t(uint, a, b) when one of a or b
is 64bit and can have a value that is larger than 2^32;
This is particularly prevelant with:
uint_var = min_t(uint, uint_var, uint64_expression);

Casts to u8 and u16 are very likely to discard significant bits.

These can be detected at compile time by changing min_t(), for example:
#define CHECK_SIZE(fn, type, val) \
BUILD_BUG_ON_MSG(sizeof (val) > sizeof (type) && \
!statically_true(((val) >> 8 * (sizeof (type) - 1)) < 256), \
fn "() significant bits of '" #val "' may be discarded")

#define min_t(type, x, y) ({ \
CHECK_SIZE("min_t", type, x); \
CHECK_SIZE("min_t", type, y); \
__cmp_once(min, type, x, y); })

(and similar changes to max_t() and clamp_t().)

This shows up some real bugs, some unlikely bugs and some false positives.
In most cases both arguments are unsigned type (just different ones)
and min_t() can just be replaced by min().

The patches are all independant and are most of the ones needed to
get the x86-64 kernel I build to compile.
I've not tried building an allyesconfig or allmodconfig kernel.
I've also not included the patch to minmax.h itself.

I've tried to put the patches that actually fix things first.
The last one is 0009.

I gave up on fixing sched/fair.c - it is too broken for a single patch!
The patch for net/ipv4/tcp.c is also absent because do_tcp_getsockopt()
needs multiple/larger changes to make it 'sane'.

I've had to trim the 124 maintainers/lists that get_maintainer.pl finds
from 124 to under 100 to be able to send the cover letter.
The individual patches only go to the addresses found for the associated files.
That reduces the number of emails to a less unsane number.

David Laight (44):
x86/asm/bitops: Change the return type of variable__ffs() to unsigned
int
ext4: Fix saturation of 64bit inode times for old filesystems
perf: Fix branch stack callchain limit
io_uring/net: Change some dubious min_t()
ipc/msg: Fix saturation of percpu counts in msgctl_info()
bpf: Verifier, remove some unusual uses of min_t() and max_t()
net/core/flow_dissector: Fix cap of __skb_flow_dissect() return value.
net: ethtool: Use min3() instead of nested min_t(u16,...)
ipv6: __ip6_append_data() don't abuse max_t() casts
x86/crypto: ctr_crypt() use min() instead of min_t()
arch/x96/kvm: use min() instead of min_t()
block: use min() instead of min_t()
drivers/acpi: use min() instead of min_t()
drivers/char/hw_random: use min3() instead of nested min_t()
drivers/char/tpm: use min() instead of min_t()
drivers/crypto/ccp: use min() instead of min_t()
drivers/cxl: use min() instead of min_t()
drivers/gpio: use min() instead of min_t()
drivers/gpu/drm/amd: use min() instead of min_t()
drivers/i2c/busses: use min() instead of min_t()
drivers/net/ethernet/realtek: use min() instead of min_t()
drivers/nvme: use min() instead of min_t()
arch/x86/mm: use min() instead of min_t()
drivers/nvmem: use min() instead of min_t()
drivers/pci: use min() instead of min_t()
drivers/scsi: use min() instead of min_t()
drivers/tty/vt: use umin() instead of min_t(u16, ...) for row/col
limits
drivers/usb/storage: use min() instead of min_t()
drivers/xen: use min() instead of min_t()
fs: use min() or umin() instead of min_t()
block: bvec.h: use min() instead of min_t()
nodemask: use min() instead of min_t()
ipc: use min() instead of min_t()
bpf: use min() instead of min_t()
bpf_trace: use min() instead of min_t()
lib/bucket_locks: use min() instead of min_t()
lib/crypto/mpi: use min() instead of min_t()
lib/dynamic_queue_limits: use max() instead of max_t()
mm: use min() instead of min_t()
net: Don't pass bitfields to max_t()
net/core: Change loop conditions so min() can be used
net: use min() instead of min_t()
net/netlink: Use umin() to avoid min_t(int, ...) discarding high bits
net/mptcp: Change some dubious min_t(int, ...) to min()

arch/x86/crypto/aesni-intel_glue.c | 3 +-
arch/x86/include/asm/bitops.h | 18 +++++-------
arch/x86/kvm/emulate.c | 3 +-
arch/x86/kvm/lapic.c | 2 +-
arch/x86/kvm/mmu/mmu.c | 2 +-
arch/x86/mm/pat/set_memory.c | 12 ++++----
block/blk-iocost.c | 6 ++--
block/blk-settings.c | 2 +-
block/partitions/efi.c | 3 +-
drivers/acpi/property.c | 2 +-
drivers/char/hw_random/core.c | 2 +-
drivers/char/tpm/tpm1-cmd.c | 2 +-
drivers/char/tpm/tpm_tis_core.c | 4 +--
drivers/crypto/ccp/ccp-dev.c | 2 +-
drivers/cxl/core/mbox.c | 2 +-
drivers/gpio/gpiolib-acpi-core.c | 2 +-
.../gpu/drm/amd/amdgpu/amdgpu_doorbell_mgr.c | 4 +--
drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 2 +-
.../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +-
drivers/i2c/busses/i2c-designware-master.c | 2 +-
drivers/net/ethernet/realtek/r8169_main.c | 3 +-
drivers/nvme/host/pci.c | 3 +-
drivers/nvme/host/zns.c | 3 +-
drivers/nvmem/core.c | 2 +-
drivers/pci/probe.c | 3 +-
drivers/scsi/hosts.c | 2 +-
drivers/tty/vt/selection.c | 9 +++---
drivers/usb/storage/protocol.c | 3 +-
drivers/xen/grant-table.c | 2 +-
fs/buffer.c | 2 +-
fs/exec.c | 2 +-
fs/ext4/ext4.h | 2 +-
fs/ext4/mballoc.c | 3 +-
fs/ext4/resize.c | 2 +-
fs/ext4/super.c | 2 +-
fs/fat/dir.c | 4 +--
fs/fat/file.c | 3 +-
fs/fuse/dev.c | 2 +-
fs/fuse/file.c | 8 ++---
fs/splice.c | 2 +-
include/linux/bvec.h | 3 +-
include/linux/nodemask.h | 9 +++---
include/linux/perf_event.h | 2 +-
include/net/tcp_ecn.h | 5 ++--
io_uring/net.c | 6 ++--
ipc/mqueue.c | 4 +--
ipc/msg.c | 6 ++--
kernel/bpf/core.c | 4 +--
kernel/bpf/log.c | 2 +-
kernel/bpf/verifier.c | 29 +++++++------------
kernel/trace/bpf_trace.c | 2 +-
lib/bucket_locks.c | 2 +-
lib/crypto/mpi/mpicoder.c | 2 +-
lib/dynamic_queue_limits.c | 2 +-
mm/gup.c | 4 +--
mm/memblock.c | 2 +-
mm/memory.c | 2 +-
mm/percpu.c | 2 +-
mm/truncate.c | 3 +-
mm/vmscan.c | 2 +-
net/core/datagram.c | 6 ++--
net/core/flow_dissector.c | 7 ++---
net/core/net-sysfs.c | 3 +-
net/core/skmsg.c | 4 +--
net/ethtool/cmis_cdb.c | 7 ++---
net/ipv4/fib_trie.c | 2 +-
net/ipv4/tcp_input.c | 4 +--
net/ipv4/tcp_output.c | 5 ++--
net/ipv4/tcp_timer.c | 4 +--
net/ipv6/addrconf.c | 8 ++---
net/ipv6/ip6_output.c | 7 +++--
net/ipv6/ndisc.c | 5 ++--
net/mptcp/protocol.c | 8 ++---
net/netlink/genetlink.c | 9 +++---
net/packet/af_packet.c | 2 +-
net/unix/af_unix.c | 4 +--
76 files changed, 141 insertions(+), 176 deletions(-)

--
2.39.5

[Jakub Kicinski]

On Wed, 19 Nov 2025 22:40:56 +0000 david.lai...@gmail.com wrote:
> I've had to trim the 124 maintainers/lists that get_maintainer.pl finds
> from 124 to under 100 to be able to send the cover letter.
> The individual patches only go to the addresses found for the associated files.
> That reduces the number of emails to a less unsane number.

Please split the networking (9?) patches out to a separate series.
It will help you with the CC list, and help us to get this applied..

[Alan Stern]

On Wed, Nov 19, 2025 at 10:41:24PM +0000, david.lai...@gmail.com wrote:
> From: David Laight <david.lai...@gmail.com>
>
> min_t(unsigned int, a, b) casts an 'unsigned long' to 'unsigned int'.
> Use min(a, b) instead as it promotes any 'unsigned int' to 'unsigned long'
> and so cannot discard significant bits.
>
> In this case the 'unsigned long' value is small enough that the result
> is ok.
>
> Detected by an extra check added to min_t().

In fact, min_t(T, a, b) cannot go wrong as long as all the types are
unsigned and at least one of a, b has type T or smaller. Of course, in
this situation there's no reason not to simply use min(). (And if both
a and b have types larger than T, why would someone use min_t() like
this in the first place?)

Regardless, the patch is fine with me.

Acked-by: Alan Stern <st...@rowland.harvard.edu>

Alan Stern

[David Laight]

On Wed, 19 Nov 2025 21:59:42 -0500
Alan Stern <st...@rowland.harvard.edu> wrote:

> On Wed, Nov 19, 2025 at 10:41:24PM +0000, david.lai...@gmail.com wrote:
> > From: David Laight <david.lai...@gmail.com>
> >
> > min_t(unsigned int, a, b) casts an 'unsigned long' to 'unsigned int'.
> > Use min(a, b) instead as it promotes any 'unsigned int' to 'unsigned long'
> > and so cannot discard significant bits.
> >
> > In this case the 'unsigned long' value is small enough that the result
> > is ok.
> >
> > Detected by an extra check added to min_t().
>
> In fact, min_t(T, a, b) cannot go wrong as long as all the types are
> unsigned and at least one of a, b has type T or smaller.

That is backwards, both a and b have to have types at least as large
as T (or rather values that will fit in T).
- which is exactly what people keep getting wrong.
Consider:
u32 a = 4;
u64 b = 0x100000001ull;
then:
min_t(u32, a, b)
has value 1 not 4.

David

[Alan Stern]

On Thu, Nov 20, 2025 at 09:18:02AM +0000, David Laight wrote:
> On Wed, 19 Nov 2025 21:59:42 -0500
> Alan Stern <st...@rowland.harvard.edu> wrote:
>
> > On Wed, Nov 19, 2025 at 10:41:24PM +0000, david.lai...@gmail.com wrote:
> > > From: David Laight <david.lai...@gmail.com>
> > >
> > > min_t(unsigned int, a, b) casts an 'unsigned long' to 'unsigned int'.
> > > Use min(a, b) instead as it promotes any 'unsigned int' to 'unsigned long'
> > > and so cannot discard significant bits.
> > >
> > > In this case the 'unsigned long' value is small enough that the result
> > > is ok.
> > >
> > > Detected by an extra check added to min_t().
> >
> > In fact, min_t(T, a, b) cannot go wrong as long as all the types are
> > unsigned and at least one of a, b has type T or smaller.
>
> That is backwards, both a and b have to have types at least as large
> as T (or rather values that will fit in T).
> - which is exactly what people keep getting wrong.
> Consider:
> u32 a = 4;
> u64 b = 0x100000001ull;
> then:
> min_t(u32, a, b)
> has value 1 not 4.

You are right. For some reason I was thinking that the comparison took
place before the casts, which doesn't make any sense.

Alan Stern

[Jens Axboe]

On Wed, 19 Nov 2025 22:40:56 +0000, david.lai...@gmail.com wrote:
> It in not uncommon for code to use min_t(uint, a, b) when one of a or b
> is 64bit and can have a value that is larger than 2^32;
> This is particularly prevelant with:
> uint_var = min_t(uint, uint_var, uint64_expression);
>
> Casts to u8 and u16 are very likely to discard significant bits.
>

> [...]

Applied, thanks!

[12/44] block: use min() instead of min_t()
commit: 9420e720ad192c53c8d2803c5a2313b2d586adbd

Best regards,
--
Jens Axboe

[Lorenzo Stoakes]

On Wed, Nov 19, 2025 at 10:40:56PM +0000, david.lai...@gmail.com wrote:
> From: David Laight <david.lai...@gmail.com>
>
> It in not uncommon for code to use min_t(uint, a, b) when one of a or b
> is 64bit and can have a value that is larger than 2^32;
> This is particularly prevelant with:
> uint_var = min_t(uint, uint_var, uint64_expression);
>
> Casts to u8 and u16 are very likely to discard significant bits.
>
> These can be detected at compile time by changing min_t(), for example:
> #define CHECK_SIZE(fn, type, val) \
> BUILD_BUG_ON_MSG(sizeof (val) > sizeof (type) && \
> !statically_true(((val) >> 8 * (sizeof (type) - 1)) < 256), \
> fn "() significant bits of '" #val "' may be discarded")
>
> #define min_t(type, x, y) ({ \
> CHECK_SIZE("min_t", type, x); \
> CHECK_SIZE("min_t", type, y); \
> __cmp_once(min, type, x, y); })
>
> (and similar changes to max_t() and clamp_t().)

Have we made sure that the introduction of these don't cause a combinatorial
explosion like previous min()/max() changes did?

>
> This shows up some real bugs, some unlikely bugs and some false positives.
> In most cases both arguments are unsigned type (just different ones)
> and min_t() can just be replaced by min().
>
> The patches are all independant and are most of the ones needed to
> get the x86-64 kernel I build to compile.
> I've not tried building an allyesconfig or allmodconfig kernel.

Well I have a beefy box at my disposal so tried thiese for you :)

Both allyesconfig & allmodconfig works fine for x86-64 (I tried both for good
measure)

> I've also not included the patch to minmax.h itself.
>
> I've tried to put the patches that actually fix things first.
> The last one is 0009.
>
> I gave up on fixing sched/fair.c - it is too broken for a single patch!
> The patch for net/ipv4/tcp.c is also absent because do_tcp_getsockopt()
> needs multiple/larger changes to make it 'sane'.

I guess this isn't broken per se there just retain min_t()/max_t() right?

[Herbert Xu]

On Wed, Nov 19, 2025 at 10:40:56PM +0000, david.lai...@gmail.com wrote:

Patches 10,14,16,37 applied. Thanks.
--
Email: Herbert Xu <her...@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt