mtd: jedec_probe: Fix crash in jedec_read_mfr()

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Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=87a73eb5b56fd6e07c8e499fe8608ef2d8912b82
Commit:     87a73eb5b56fd6e07c8e499fe8608ef2d8912b82
Parent:     2b1b1b4ac716fd929a2d221bd4ade62263bed915
Author:     Linus Walleij <linus.walleij at linaro.org>
AuthorDate: Sat Mar 3 23:29:03 2018 +0100
Committer:  Boris Brezillon <boris.brezillon at bootlin.com>
CommitDate: Thu Mar 29 19:29:06 2018 +0200

    mtd: jedec_probe: Fix crash in jedec_read_mfr()
    
    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.
    
    Fixes: 5c9c11e1c47c ("[MTD] [NOR] Add support for flash chips with ID in bank other than 0")
    Cc: <stable at vger.kernel.org>
    Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
    Signed-off-by: Boris Brezillon <boris.brezillon at bootlin.com>
---
 drivers/mtd/chips/jedec_probe.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/mtd/chips/jedec_probe.c b/drivers/mtd/chips/jedec_probe.c
index 7c0b27d132b1..b479bd81120b 100644
--- a/drivers/mtd/chips/jedec_probe.c
+++ b/drivers/mtd/chips/jedec_probe.c
@@ -1889,6 +1889,8 @@ static inline u32 jedec_read_mfr(struct map_info *map, uint32_t base,
 	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);