From eca6f534e61919b28fb21aafbd1c2983deae75be Mon Sep 17 00:00:00 2001 From: Vegard Nossum Date: Fri, 18 Sep 2009 13:05:45 -0700 Subject: fs: fix overflow in sys_mount() for in-kernel calls sys_mount() reads/copies a whole page for its "type" parameter. When do_mount_root() passes a kernel address that points to an object which is smaller than a whole page, copy_mount_options() will happily go past this memory object, possibly dereferencing "wild" pointers that could be in any state (hence the kmemcheck warning, which shows that parts of the next page are not even allocated). (The likelihood of something going wrong here is pretty low -- first of all this only applies to kernel calls to sys_mount(), which are mostly found in the boot code. Secondly, I guess if the page was not mapped, exact_copy_from_user() _would_ in fact handle it correctly because of its access_ok(), etc. checks.) But it is much nicer to avoid the dubious reads altogether, by stopping as soon as we find a NUL byte. Is there a good reason why we can't do something like this, using the already existing strndup_from_user()? [akpm@linux-foundation.org: make copy_mount_string() static] [AV: fix compat mount breakage, which involves undoing akpm's change above] Reported-by: Ingo Molnar Signed-off-by: Vegard Nossum Cc: Al Viro Cc: Pekka Enberg Signed-off-by: Andrew Morton Signed-off-by: al --- fs/compat.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-) (limited to 'fs/compat.c') diff --git a/fs/compat.c b/fs/compat.c index 3aa48834a22..d576b552e8e 100644 --- a/fs/compat.c +++ b/fs/compat.c @@ -768,13 +768,13 @@ asmlinkage long compat_sys_mount(char __user * dev_name, char __user * dir_name, char __user * type, unsigned long flags, void __user * data) { - unsigned long type_page; + char *kernel_type; unsigned long data_page; - unsigned long dev_page; + char *kernel_dev; char *dir_page; int retval; - retval = copy_mount_options (type, &type_page); + retval = copy_mount_string(type, &kernel_type); if (retval < 0) goto out; @@ -783,38 +783,38 @@ asmlinkage long compat_sys_mount(char __user * dev_name, char __user * dir_name, if (IS_ERR(dir_page)) goto out1; - retval = copy_mount_options (dev_name, &dev_page); + retval = copy_mount_string(dev_name, &kernel_dev); if (retval < 0) goto out2; - retval = copy_mount_options (data, &data_page); + retval = copy_mount_options(data, &data_page); if (retval < 0) goto out3; retval = -EINVAL; - if (type_page && data_page) { - if (!strcmp((char *)type_page, SMBFS_NAME)) { + if (kernel_type && data_page) { + if (!strcmp(kernel_type, SMBFS_NAME)) { do_smb_super_data_conv((void *)data_page); - } else if (!strcmp((char *)type_page, NCPFS_NAME)) { + } else if (!strcmp(kernel_type, NCPFS_NAME)) { do_ncp_super_data_conv((void *)data_page); - } else if (!strcmp((char *)type_page, NFS4_NAME)) { + } else if (!strcmp(kernel_type, NFS4_NAME)) { if (do_nfs4_super_data_conv((void *) data_page)) goto out4; } } - retval = do_mount((char*)dev_page, dir_page, (char*)type_page, + retval = do_mount(kernel_dev, dir_page, kernel_type, flags, (void*)data_page); out4: free_page(data_page); out3: - free_page(dev_page); + kfree(kernel_dev); out2: putname(dir_page); out1: - free_page(type_page); + kfree(kernel_type); out: return retval; } -- cgit v1.2.3