4.4-stable review patch. If anyone has any objections, please let me know.
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From: Willy Tarreau w@1wt.eu
commit 7f7ccc2ccc2e70c6054685f5e3522efa81556830 upstream.
proc_pid_cmdline_read() and environ_read() directly access the target process' VM to retrieve the command line and environment. If this process remaps these areas onto a file via mmap(), the requesting process may experience various issues such as extra delays if the underlying device is slow to respond.
Let's simply refuse to access file-backed areas in these functions. For this we add a new FOLL_ANON gup flag that is passed to all calls to access_remote_vm(). The code already takes care of such failures (including unmapped areas). Accesses via /proc/pid/mem were not changed though.
This was assigned CVE-2018-1120.
Note for stable backports: the patch may apply to kernels prior to 4.11 but silently miss one location; it must be checked that no call to access_remote_vm() keeps zero as the last argument.
Reported-by: Qualys Security Advisory qsa@qualys.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Andy Lutomirski luto@amacapital.net Cc: Oleg Nesterov oleg@redhat.com Signed-off-by: Willy Tarreau w@1wt.eu Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [bwh: Backported to 4.4: - Update the extra call to access_remote_vm() from proc_pid_cmdline_read() - Adjust context] Signed-off-by: Ben Hutchings ben.hutchings@codethink.co.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/proc/base.c | 10 +++++----- include/linux/mm.h | 1 + mm/gup.c | 3 +++ 3 files changed, 9 insertions(+), 5 deletions(-)
--- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -254,7 +254,7 @@ static ssize_t proc_pid_cmdline_read(str * Inherently racy -- command line shares address space * with code and data. */ - rv = access_remote_vm(mm, arg_end - 1, &c, 1, 0); + rv = access_remote_vm(mm, arg_end - 1, &c, 1, FOLL_ANON); if (rv <= 0) goto out_free_page;
@@ -272,7 +272,7 @@ static ssize_t proc_pid_cmdline_read(str int nr_read;
_count = min3(count, len, PAGE_SIZE); - nr_read = access_remote_vm(mm, p, page, _count, 0); + nr_read = access_remote_vm(mm, p, page, _count, FOLL_ANON); if (nr_read < 0) rv = nr_read; if (nr_read <= 0) @@ -307,7 +307,7 @@ static ssize_t proc_pid_cmdline_read(str bool final;
_count = min3(count, len, PAGE_SIZE); - nr_read = access_remote_vm(mm, p, page, _count, 0); + nr_read = access_remote_vm(mm, p, page, _count, FOLL_ANON); if (nr_read < 0) rv = nr_read; if (nr_read <= 0) @@ -356,7 +356,7 @@ skip_argv: bool final;
_count = min3(count, len, PAGE_SIZE); - nr_read = access_remote_vm(mm, p, page, _count, 0); + nr_read = access_remote_vm(mm, p, page, _count, FOLL_ANON); if (nr_read < 0) rv = nr_read; if (nr_read <= 0) @@ -1006,7 +1006,7 @@ static ssize_t environ_read(struct file max_len = min_t(size_t, PAGE_SIZE, count); this_len = min(max_len, this_len);
- retval = access_remote_vm(mm, (env_start + src), page, this_len, 0); + retval = access_remote_vm(mm, (env_start + src), page, this_len, FOLL_ANON);
if (retval <= 0) { ret = retval; --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2120,6 +2120,7 @@ static inline struct page *follow_page(s #define FOLL_TRIED 0x800 /* a retry, previous pass started an IO */ #define FOLL_MLOCK 0x1000 /* lock present pages */ #define FOLL_COW 0x4000 /* internal GUP flag */ +#define FOLL_ANON 0x8000 /* don't do file mappings */
typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr, void *data); --- a/mm/gup.c +++ b/mm/gup.c @@ -368,6 +368,9 @@ static int check_vma_flags(struct vm_are if (vm_flags & (VM_IO | VM_PFNMAP)) return -EFAULT;
+ if (gup_flags & FOLL_ANON && !vma_is_anonymous(vma)) + return -EFAULT; + if (gup_flags & FOLL_WRITE) { if (!(vm_flags & VM_WRITE)) { if (!(gup_flags & FOLL_FORCE))