[PATCH 6.12 191/567] char: applicom: fix NULL pointer dereference in ac_ioctl

Greg Kroah-Hartman
2026-01-06T17:24:49Z

From: Tianchu Chen <flynnnchen@tencent.com>

commit 82d12088c297fa1cef670e1718b3d24f414c23f7 upstream.

Discovered by Atuin - Automated Vulnerability Discovery Engine.

In ac_ioctl, the validation of IndexCard and the check for a valid
RamIO pointer are skipped when cmd is 6. However, the function
unconditionally executes readb(apbs[IndexCard].RamIO + VERS) at the
end.

If cmd is 6, IndexCard may reference a board that does not exist
(where RamIO is NULL), leading to a NULL pointer dereference.

Fix this by skipping the readb access when cmd is 6, as this
command is a global information query and does not target a specific
board context.

Signed-off-by: Tianchu Chen <flynnnchen@tencent.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: stable <stable@kernel.org>
Link: https://patch.msgid.link/20251128155323.a786fde92ebb926cbe96fcb1@linux.dev
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/applicom.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/char/applicom.c
+++ b/drivers/char/applicom.c
@@ -835,7 +835,10 @@ static long ac_ioctl(struct file *file,
ret = -ENOTTY;
break;
}
- Dummy = readb(apbs[IndexCard].RamIO + VERS);
+
+ if (cmd != 6)
+ Dummy = readb(apbs[IndexCard].RamIO + VERS);
+
kfree(adgl);
mutex_unlock(&ac_mutex);
return ret;