On Jun 10, 2015, at 3:52 AM, Dan Carpenter wrote: > On Wed, Jun 10, 2015 at 12:41:23AM -0400, green@xxxxxxxxxxxxxx wrote: >> From: Oleg Drokin <green@xxxxxxxxxxxxxx> >> >> strncpy_from_user could return negative values on error, >> so need to take those into account. >> Since ll_getname is used to get a single component name from userspace >> to transfer to server as-is, there's no need to allocate 4k buffer >> as done by __getname. Allocate NAME_MAX+1 buffer instead to ensure >> we have enough for a null terminated max valid length buffer. >> >> This was discovered by Al Viro in https://lkml.org/lkml/2015/4/11/243 >> >> Signed-off-by: Oleg Drokin <green@xxxxxxxxxxxxxx> >> --- >> drivers/staging/lustre/lustre/llite/dir.c | 20 +++++++++++--------- >> 1 file changed, 11 insertions(+), 9 deletions(-) >> >> diff --git a/drivers/staging/lustre/lustre/llite/dir.c b/drivers/staging/lustre/lustre/llite/dir.c >> index 87a042c..e0b9043 100644 >> --- a/drivers/staging/lustre/lustre/llite/dir.c >> +++ b/drivers/staging/lustre/lustre/llite/dir.c >> @@ -1213,29 +1213,31 @@ out: >> return rc; >> } >> >> -static char * >> -ll_getname(const char __user *filename) >> +/* This function tries to get a single name component, >> + * to send to the server. No actual path traversal involved, >> + * so we limit to NAME_MAX */ >> +static char *ll_getname(const char __user *filename) >> { >> int ret = 0, len; >> - char *tmp = __getname(); >> + char *tmp = kzalloc(NAME_MAX + 1, GFP_KERNEL); > > Doing allocations in the declaration block is rare in the kernel but it > accounts for around a quarter of the missing NULL checks and many memory > leaks in the kbuild zero day bot testing. It's a bad idea and some > subsystems ban the practice, but Greg is fine with it so I'm not going > to complain. Fair. I can redo this. >> >> if (!tmp) >> return ERR_PTR(-ENOMEM); >> >> - len = strncpy_from_user(tmp, filename, PATH_MAX); >> - if (len == 0) >> + len = strncpy_from_user(tmp, filename, NAME_MAX); >> + if (len < 0) >> + ret = len; >> + else if (len == 0) >> ret = -ENOENT; >> - else if (len > PATH_MAX) >> - ret = -ENAMETOOLONG; > > I don't like how this does silent truncation. strncpy_from_user() > return -EFAULT if we run into unmapped memory. Otherwise if the user > supplies a too long name it returns len == PATH_MAX. (I think, the > documentation for this function is hard to understand). > > Of course, the check was never true in the original code… Right. It's no big deal to ask for NAME_MAX+1 and then restore the len > NAME_MAX check and return -ENAMETOOLONG in that case. Then the silent truncate is gone and logic wise we don't care all that much either way, I imagine. Bye, Oleg _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
