linux-kernel - [PATCH] coredump: fix dumping through pipes

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Date:	Sun,  5 Jun 2016 13:55:25 +0200
From:	Mateusz Guzik <mguzik@...hat.com>
To:	Omar Sandoval <osandov@...com>
Cc:	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCH] coredump: fix dumping through pipes

The offset in the core file used to be tracked with ->written field of
the coredump_params structure. Commit a0083939510 ("get rid of
coredump_params->written") replaced all its uses with file->f_pos.

However, ->f_pos is not maintained for pipes which leads to breakage.

Restore explicit tracking of the offset in coredump_params. Introduce
->pos field for this purpose since ->written was already reused.

Reported-by: Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>
Signed-off-by: Mateusz Guzik <mguzik@...hat.com>
---
 arch/powerpc/platforms/cell/spufs/coredump.c | 2 +-
 fs/binfmt_elf.c                              | 2 +-
 fs/binfmt_elf_fdpic.c                        | 2 +-
 fs/coredump.c                                | 4 +++-
 include/linux/binfmts.h                      | 1 +
 5 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/platforms/cell/spufs/coredump.c b/arch/powerpc/platforms/cell/spufs/coredump.c
index 84fb984..85c85eb 100644
--- a/arch/powerpc/platforms/cell/spufs/coredump.c
+++ b/arch/powerpc/platforms/cell/spufs/coredump.c
@@ -172,7 +172,7 @@ static int spufs_arch_write_note(struct spu_context *ctx, int i,
 	if (rc < 0)
 		goto out;
 
-	skip = roundup(cprm->file->f_pos - total + sz, 4) - cprm->file->f_pos;
+	skip = roundup(cprm->pos - total + sz, 4) - cprm->pos;
 	if (!dump_skip(cprm, skip))
 		goto Eio;
 out:
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index e158b22..a7a28110 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -2275,7 +2275,7 @@ static int elf_core_dump(struct coredump_params *cprm)
 		goto end_coredump;
 
 	/* Align to page */
-	if (!dump_skip(cprm, dataoff - cprm->file->f_pos))
+	if (!dump_skip(cprm, dataoff - cprm->pos))
 		goto end_coredump;
 
 	for (i = 0, vma = first_vma(current, gate_vma); vma != NULL;
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index 71ade0e..2035893 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -1787,7 +1787,7 @@ static int elf_fdpic_core_dump(struct coredump_params *cprm)
 				goto end_coredump;
 	}
 
-	if (!dump_skip(cprm, dataoff - cprm->file->f_pos))
+	if (!dump_skip(cprm, dataoff - cprm->pos))
 		goto end_coredump;
 
 	if (!elf_fdpic_dump_segments(cprm))
diff --git a/fs/coredump.c b/fs/coredump.c
index 38a7ab8..281b768 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -794,6 +794,7 @@ int dump_emit(struct coredump_params *cprm, const void *addr, int nr)
 			return 0;
 		file->f_pos = pos;
 		cprm->written += n;
+		cprm->pos += n;
 		nr -= n;
 	}
 	return 1;
@@ -808,6 +809,7 @@ int dump_skip(struct coredump_params *cprm, size_t nr)
 		if (dump_interrupted() ||
 		    file->f_op->llseek(file, nr, SEEK_CUR) < 0)
 			return 0;
+		cprm->pos += nr;
 		return 1;
 	} else {
 		while (nr > PAGE_SIZE) {
@@ -822,7 +824,7 @@ EXPORT_SYMBOL(dump_skip);
 
 int dump_align(struct coredump_params *cprm, int align)
 {
-	unsigned mod = cprm->file->f_pos & (align - 1);
+	unsigned mod = cprm->pos & (align - 1);
 	if (align & (align - 1))
 		return 0;
 	return mod ? dump_skip(cprm, align - mod) : 1;
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 576e463..314b3ca 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -65,6 +65,7 @@ struct coredump_params {
 	unsigned long limit;
 	unsigned long mm_flags;
 	loff_t written;
+	loff_t pos;
 };
 
 /*
-- 
1.8.3.1