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9f32f38265
The SLAVE-path helpers buffer_to_user() and buffer_from_user() copy
'count' bytes into/out of the fixed-size kern_buf (size_buf ==
PCI_BUF_SIZE == 0x20000, 128 KiB) using *ppos as the offset, without
bounding *ppos + count against size_buf.
vme_user_write()/vme_user_read() only clamp count to the VME window size
(image_size = vme_get_size(resource)), which VME_SET_SLAVE sets from the
user-supplied slave.size -- validated against the VME address space (up
to VME_A32_MAX = 4 GiB), not against PCI_BUF_SIZE. When the window
exceeds 128 KiB, a write()/read() copies past the kern_buf allocation.
Clamp count against size_buf in both helpers, with an early return when
*ppos is already at/after the buffer end. *ppos is >= 0 here (the caller
rejects negative offsets), so size_buf - *ppos cannot wrap. This mirrors
the existing clamp in the MASTER-path helpers resource_to_user() /
resource_from_user(), and matches the read()/write() convention of a
short transfer at end-of-buffer.
Found by static analysis (CodeQL taint tracking + CBMC bounded model
checking) and confirmed dynamically under KASAN with the vme_fake bridge:
BUG: KASAN: slab-out-of-bounds in _copy_from_user+0x2d/0x80
Write of size 262144 at addr ffff888004100000 by task trigger/68
_copy_from_user+0x2d/0x80
vme_user_write+0x13e/0x240 [vme_user]
vfs_write+0x1b8/0x7a0
ksys_write+0xb8/0x150
Fixes: f00a86d98a ("Staging: vme: add VME userspace driver")
Cc: stable <stable@kernel.org>
Signed-off-by: Michael Tautschnig <tautschn@amazon.com>
Link: https://patch.msgid.link/20260618114709.72499-1-tautschn@amazon.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>