| From foo@baz Mon Sep 24 09:32:39 CEST 2018 |
| From: Jann Horn <jannh@google.com> |
| Date: Sat, 7 Jul 2018 05:37:22 +0200 |
| Subject: mtdchar: fix overflows in adjustment of `count` |
| |
| From: Jann Horn <jannh@google.com> |
| |
| [ Upstream commit 6c6bc9ea84d0008024606bf5ba10519e20d851bf ] |
| |
| The first checks in mtdchar_read() and mtdchar_write() attempt to limit |
| `count` such that `*ppos + count <= mtd->size`. However, they ignore the |
| possibility of `*ppos > mtd->size`, allowing the calculation of `count` to |
| wrap around. `mtdchar_lseek()` prevents seeking beyond mtd->size, but the |
| pread/pwrite syscalls bypass this. |
| |
| I haven't found any codepath on which this actually causes dangerous |
| behavior, but it seems like a sensible change anyway. |
| |
| Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") |
| Signed-off-by: Jann Horn <jannh@google.com> |
| Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com> |
| Signed-off-by: Sasha Levin <alexander.levin@microsoft.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| drivers/mtd/mtdchar.c | 10 +++++++--- |
| 1 file changed, 7 insertions(+), 3 deletions(-) |
| |
| --- a/drivers/mtd/mtdchar.c |
| +++ b/drivers/mtd/mtdchar.c |
| @@ -160,8 +160,12 @@ static ssize_t mtdchar_read(struct file |
| |
| pr_debug("MTD_read\n"); |
| |
| - if (*ppos + count > mtd->size) |
| - count = mtd->size - *ppos; |
| + if (*ppos + count > mtd->size) { |
| + if (*ppos < mtd->size) |
| + count = mtd->size - *ppos; |
| + else |
| + count = 0; |
| + } |
| |
| if (!count) |
| return 0; |
| @@ -246,7 +250,7 @@ static ssize_t mtdchar_write(struct file |
| |
| pr_debug("MTD_write\n"); |
| |
| - if (*ppos == mtd->size) |
| + if (*ppos >= mtd->size) |
| return -ENOSPC; |
| |
| if (*ppos + count > mtd->size) |
