On 20/10/14 22:38, Hartley Sweeten wrote:
On Monday, October 20, 2014 7:11 AM, Ian Abbott wrote:As a follow-up to commit 6cab7a37f5c04 ("staging: comedi: (regression) channel list must be set for COMEDI_CMD ioctl"), Hartley Sweeten pointed out another couple of bugs stemming from commit 6cab7a37f5c04 ("staging: comedi: comedi_fops: introduce __comedi_get_user_chanlist()"). Firstly, `do_cmdtest_ioctl()` never frees the kernel copy of the user chanlist allocated by `__comedi_get_user_chanlist()`, so that memory is leaked. Fix it by freeing the allocated kernel memory pointed to by `cmd.chanlist` before that pointer is overwritten with its original pointer to user memory before `cmd` is copied back to user-space. Secondly, if `__comedi_get_user_chanlist()` returns an error, `cmd->chanlist` is left unchanged and in fact will be a pointer to user memory. This causes `do_cmd_ioctl()` to `goto cleanup` and call `do_become_nonbusy()` which would attempt to free the memory pointed to by the user-space pointer. Fix it by setting `cmd->chanlist` to NULL at the start of `__comedi_get_user_chanlist()`. Fixes: c6cd0eefb27b ("staging: comedi: comedi_fops: introduce __comedi_get_user_chanlist()") Reported-by: H Hartley Sweeten <hsweeten@xxxxxxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # 3.15.y 3.16.y 3.17.y: 6cab7a37f5c04 Cc: <stable@xxxxxxxxxxxxxxx> # 3.15.y 3.16.y 3.17.y --- Greg, this patch applies to your "staging-linus" branch. --- drivers/staging/comedi/comedi_fops.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c index a9b7fe5..a1788e8 100644 --- a/drivers/staging/comedi/comedi_fops.c +++ b/drivers/staging/comedi/comedi_fops.c @@ -1462,6 +1462,7 @@ static int __comedi_get_user_chanlist(struct comedi_device *dev, unsigned int *chanlist; int ret; + cmd->chanlist = NULL; chanlist = memdup_user(user_chanlist, cmd->chanlist_len * sizeof(unsigned int)); if (IS_ERR(chanlist))I don't think this covers all the problems in your second issue above. It does fix the attempt to free the memory pointed to by the user-space pointer if the memdub_user() fails. But in do_cmd_ioctl() we still have an issue if the s->do_cmdtest() fails or the CMDF_BOGUS flag is set. There we restore the users cmd.chanlist pointer to allow copy_to_user() to return the cmd/ But the kernel allocated chanlist is not freed. The goto cleanup will again try to free the user-space pointer.
No, 'async->cmd' is copied (via struct assignment) to local variable 'cmd' and it is the local 'cmd.chanlist' pointer that is set to the original user-space pointer and the local 'cmd' that is copied back to user-space. 'async->cmd.chanlist' still points to the kernel copy of the chanlist that gets cleaned up by 'goto cleanup' / 'do_become_nonbusy().
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