linux-kernel - [PATCH v4 39/66] binfmt_elf: Take the mmap lock when walking the VMA list

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Message-ID: <20211201142918.921493-40-Liam.Howlett@oracle.com>
Date:   Wed, 1 Dec 2021 14:30:08 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Rik van Riel <riel@...riel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michel Lespinasse <walken.cr@...il.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Minchan Kim <minchan@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Rom Lemarchand <romlem@...gle.com>,
        Liam Howlett <liam.howlett@...cle.com>
Subject: [PATCH v4 39/66] binfmt_elf: Take the mmap lock when walking the VMA
 list

From: "Matthew Wilcox (Oracle)" <willy@...radead.org>

I'm not sure if the VMA list can change under us, but dump_vma_snapshot()
is very careful to take the mmap_lock in write mode.  We only need to
take it in read mode here as we do not care if the size of the stack
VMA changes underneath us.

If it can be changed underneath us, this is a potential use-after-free
for a multithreaded process which is dumping core.

Fixes: 2aa362c49c31 ("coredump: extend core dump note section to contain file names of mapped files")
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 fs/binfmt_elf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index d41cca755ff9..5915518c8a1d 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1652,6 +1652,7 @@ static int fill_files_note(struct memelfnote *note)
 	name_base = name_curpos = ((char *)data) + names_ofs;
 	remaining = size - names_ofs;
 	count = 0;
+	mmap_read_lock(mm);
 	for_each_vma(vmi, vma) {
 		struct file *file;
 		const char *filename;
@@ -1662,6 +1663,7 @@ static int fill_files_note(struct memelfnote *note)
 		filename = file_path(file, name_curpos, remaining);
 		if (IS_ERR(filename)) {
 			if (PTR_ERR(filename) == -ENAMETOOLONG) {
+				mmap_read_unlock(mm);
 				kvfree(data);
 				size = size * 5 / 4;
 				goto alloc;
@@ -1681,6 +1683,7 @@ static int fill_files_note(struct memelfnote *note)
 		*start_end_ofs++ = vma->vm_pgoff;
 		count++;
 	}
+	mmap_read_unlock(mm);
 
 	/* Now we know exact count of files, can store it */
 	data[0] = count;
-- 
2.30.2