Patch "mtd: jedec_probe: Fix crash in jedec_read_mfr()" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

mtd: jedec_probe: Fix crash in jedec_read_mfr()

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mtd-jedec_probe-fix-crash-in-jedec_read_mfr.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Linus Walleij <[email protected]>
Date: Sat, 3 Mar 2018 23:29:03 +0100
Subject: mtd: jedec_probe: Fix crash in jedec_read_mfr()

From: Linus Walleij <[email protected]>

commit 87a73eb5b56fd6e07c8e499fe8608ef2d8912b82 upstream.

It turns out that the loop where we read manufacturer jedec_read_mfd() can under some circumstances get a CFI_MFR_CONTINUATION repeatedly, making the loop go over all banks and eventually hit the end of the map and crash because of an access violation:

Unable to handle kernel paging request at virtual address c4980000
pgd = (ptrval)
[c4980000] *pgd=03808811, *pte=00000000, *ppte=00000000
Internal error: Oops: 7 [#1] PREEMPT ARM
CPU: 0 PID: 1 Comm: swapper Not tainted 4.16.0-rc1+ #150
Hardware name: Gemini (Device Tree)
PC is at jedec_probe_chip+0x6ec/0xcd0
LR is at 0x4
pc : [<c03a2bf4>]    lr : [<00000004>]    psr: 60000013

sp : c382dd18 ip : 0000ffff fp : 00000000
r10: c0626388 r9 : 00020000 r8 : c0626340
r7 : 00000000 r6 : 00000001 r5 : c3a71afc r4 : c382dd70 r3 : 00000001 r2 : c4900000 r1 : 00000002 r0 : 00080000
Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
Control: 0000397f Table: 00004000 DAC: 00000053 Process swapper (pid: 1, stack limit = 0x(ptrval))

Fix this by breaking the loop with a return 0 if
the offset exceeds the map size.

---
 drivers/mtd/chips/jedec_probe.c |    2 ++
 1 file changed, 2 insertions(+)

@@ -1889,6 +1889,8 @@ static inline u32 jedec_read_mfr(struct
 	do {
 		uint32_t ofs = cfi_build_cmd_addr(0 + (bank << 8), map, cfi);
 		mask = (1 << (cfi->device_type * 8)) - 1;
+		if (ofs >= map->size)
+			return 0;
 		result = map_read(map, base + ofs);
 		bank++;
 	} while ((result.x[0] & mask) == CFI_MFR_CONTINUATION);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/mtd-jedec_probe-fix-crash-in-jedec_read_mfr.patch