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mm/vmalloc: fix the unchecked dereference warning in vread_iter()

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LKP reported smatch warning as below:

===================
smatch warnings:
mm/vmalloc.c:3689 vread_iter() error: we previously assumed 'vm' could be null (see line 3667)
......
06c8994626  @3667 size = vm ? get_vm_area_size(vm) : va_size(va);
......
06c8994626  @3689 else if (!(vm->flags & VM_IOREMAP))
                                 ^^^^^^^^^
Unchecked dereference
=====================

This is not a runtime bug because the possible null 'vm' in the
pointed place could only happen when flags == VMAP_BLOCK.  However, the
case 'flags == VMAP_BLOCK' should never happen and has been detected
with WARN_ON.  Please check vm_map_ram() implementation and the earlier
checking in vread_iter() at below:

                ~~~~~~~~~~~~~~~~~~~~~~~~~~
                /*
                 * VMAP_BLOCK indicates a sub-type of vm_map_ram area, need
                 * be set together with VMAP_RAM.
                 */
                WARN_ON(flags == VMAP_BLOCK);

                if (!vm && !flags)
                        continue;
                ~~~~~~~~~~~~~~~~~~~~~~~~~~

So add checking on whether 'vm' could be null when dereferencing it in
vread_iter(). This mutes smatch complaint.

Link: https://lkml.kernel.org/r/ZTCURc8ZQE+KrTvS@MiWiFi-R3L-srv
Link: https://lkml.kernel.org/r/ZS/2k6DIMd0tZRgK@MiWiFi-R3L-srv
Signed-off-by: Baoquan He <bhe@redhat.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202310171600.WCrsOwFj-lkp@intel.com/
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Philip Li <philip.li@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Baoquan He 2023-10-18 22:50:14 +08:00 committed by Andrew Morton
parent cb61dad80f
commit ca6c2ce1b4
1 changed files with 1 additions and 1 deletions
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2
mm/vmalloc.c
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@ -3809,7 +3809,7 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
if (flags & VMAP_RAM)
copied = vmap_ram_vread_iter(iter, addr, n, flags);
else if (!(vm->flags & VM_IOREMAP))
else if (!(vm && (vm->flags & VM_IOREMAP)))
copied = aligned_vread_iter(iter, addr, n);
else /* IOREMAP area is treated as memory hole */
copied = zero_iter(iter, n);