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authorJann Horn <jannh@google.com>2018-07-07 05:37:22 +0200
committerBoris Brezillon <boris.brezillon@bootlin.com>2018-07-18 16:46:38 +0200
commit6c6bc9ea84d0008024606bf5ba10519e20d851bf (patch)
treed8a2b9ee1739402d40438324bb4f825a151f9394 /drivers/mtd/mtdchar.c
parentmtd: Fallback to ->_read/write() when ->_read/write_oob() is missing (diff)
downloadlinux-6c6bc9ea84d0008024606bf5ba10519e20d851bf.tar.xz
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mtdchar: fix overflows in adjustment of `count`
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>
Diffstat (limited to 'drivers/mtd/mtdchar.c')
-rw-r--r--drivers/mtd/mtdchar.c10
1 files changed, 7 insertions, 3 deletions
diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index cd67c85cc87d..02389528f622 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -160,8 +160,12 @@ static ssize_t mtdchar_read(struct file *file, char __user *buf, size_t count,
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 *file, const char __user *buf, size_t c
pr_debug("MTD_write\n");
- if (*ppos == mtd->size)
+ if (*ppos >= mtd->size)
return -ENOSPC;
if (*ppos + count > mtd->size)