[PATCH v2, 4/5] elf coredump: make offset calculation process andwriting process explicit

[Daisuke HATAYAMA]

By the next patch, elf_core_dump() and elf_fdpic_core_dump() will
support extended numbering and so will possibly produce the corefiles
with section header table.

The problem is the process of writing a file header offset of the
section header table into e_shoff field of the ELF header. ELF header
is positioned at the beginning of the corefile, while section header
at the end. So, there are two ways to do this:

 1. Seek backward to retry writing operation for ELF header
    after writing process for a whole part

 2. Make offset calculation process and writing process
    totally sequential

The clause 1. is not always possible: one cannot assume that file
system supports seek function. Consider the no_llseek case.

Therefore, this patch adopts the clause 2.

Signed-off-by: Daisuke HATAYAMA <d.hatayama@xxxxxxxxxxxxxx>
---
 fs/binfmt_elf.c       |   27 ++++++++++++++++-----------
 fs/binfmt_elf_fdpic.c |   29 ++++++++++++++++-------------
 2 files changed, 32 insertions(+), 24 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 1b7e9de..b1ded32 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1879,6 +1879,7 @@ static int elf_core_dump(struct coredump_params *cprm)
 	loff_t offset = 0, dataoff, foffset;
 	unsigned long mm_flags;
 	struct elf_note_info info;
+	struct elf_phdr *phdr4note = NULL;
 
 	/*
 	 * We no longer stop all VM operations.
@@ -1921,28 +1922,22 @@ static int elf_core_dump(struct coredump_params *cprm)
 	fs = get_fs();
 	set_fs(KERNEL_DS);
 
-	size += sizeof(*elf);
-	if (size > cprm->limit || !dump_write(cprm->file, elf, sizeof(*elf)))
-		goto end_coredump;
-
 	offset += sizeof(*elf);				/* Elf header */
 	offset += (segs + 1) * sizeof(struct elf_phdr); /* Program headers */
 	foffset = offset;
 
 	/* Write notes phdr entry */
 	{
-		struct elf_phdr phdr;
 		size_t sz = get_note_info_size(&info);
 
 		sz += elf_coredump_extra_notes_size();
 
-		fill_elf_note_phdr(&phdr, sz, offset);
-		offset += sz;
-
-		size += sizeof(phdr);
-		if (size > cprm->limit
-		    || !dump_write(cprm->file, &phdr, sizeof(phdr)))
+		phdr4note = kmalloc(sizeof(*phdr4note), GFP_KERNEL);
+		if (!phdr4note)
 			goto end_coredump;
+
+		fill_elf_note_phdr(phdr4note, sz, offset);
+		offset += sz;
 	}
 
 	dataoff = offset = roundup(offset, ELF_EXEC_PAGESIZE);
@@ -1954,6 +1949,15 @@ static int elf_core_dump(struct coredump_params *cprm)
 	 */
 	mm_flags = current->mm->flags;
 
+	size += sizeof(*elf);
+	if (size > cprm->limit || !dump_write(cprm->file, elf, sizeof(*elf)))
+		goto end_coredump;
+
+	size += sizeof(*phdr4note);
+	if (size > cprm->limit
+	    || !dump_write(cprm->file, phdr4note, sizeof(*phdr4note)))
+		goto end_coredump;
+
 	/* Write program headers for segments dump */
 	for (vma = first_vma(current, gate_vma); vma != NULL;
 			vma = next_vma(vma, gate_vma)) {
@@ -2027,6 +2031,7 @@ end_coredump:
 
 cleanup:
 	free_note_info(&info);
+	kfree(phdr4note);
 	kfree(elf);
 out:
 	return has_dumped;
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index 4c16ff6..cbfa34e 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -1588,6 +1588,7 @@ static int elf_fdpic_core_dump(struct coredump_params *cprm)
 	int thread_status_size = 0;
 	elf_addr_t *auxv;
 	unsigned long mm_flags;
+	struct elf_phdr *phdr4note = NULL;
 
 	/*
 	 * We no longer stop all VM operations.
@@ -1694,18 +1695,12 @@ static int elf_fdpic_core_dump(struct coredump_params *cprm)
 	fs = get_fs();
 	set_fs(KERNEL_DS);
 
-	size += sizeof(*elf);
-	if (size > cprm->limit
-	    || !dump_write(cprm->file, elf, sizeof(*elf)))
-		goto end_coredump;
-
 	offset += sizeof(*elf);				/* Elf header */
 	offset += (segs+1) * sizeof(struct elf_phdr);	/* Program headers */
 	foffset = offset;
 
 	/* Write notes phdr entry */
 	{
-		struct elf_phdr phdr;
 		int sz = 0;
 
 		for (i = 0; i < numnote; i++)
@@ -1713,13 +1708,12 @@ static int elf_fdpic_core_dump(struct coredump_params *cprm)
 
 		sz += thread_status_size;
 
-		fill_elf_note_phdr(&phdr, sz, offset);
-		offset += sz;
-
-		size += sizeof(phdr);
-		if (size > cprm->limit
-		    || !dump_write(cprm->file, &phdr, sizeof(phdr)))
+		phdr4note = kmalloc(sizeof(*phdr4note), GFP_KERNEL);
+		if (!phdr4note)
 			goto end_coredump;
+
+		fill_elf_note_phdr(phdr4note, sz, offset);
+		offset += sz;
 	}
 
 	/* Page-align dumped data */
@@ -1732,6 +1726,15 @@ static int elf_fdpic_core_dump(struct coredump_params *cprm)
 	 */
 	mm_flags = current->mm->flags;
 
+	size += sizeof(*elf);
+	if (size > cprm->limit || !dump_write(cprm->file, elf, sizeof(*elf)))
+		goto end_coredump;
+
+	size += sizeof(*phdr4note);
+	if (size > cprm->limit
+	    || !dump_write(cprm->file, phdr4note, sizeof(*phdr4note)))
+		goto end_coredump;
+
 	/* write program headers for segments dump */
 	for (vma = current->mm->mmap; vma; vma = vma->vm_next) {
 		struct elf_phdr phdr;
@@ -1803,7 +1806,7 @@ cleanup:
 		list_del(tmp);
 		kfree(list_entry(tmp, struct elf_thread_status, list));
 	}
-
+	kfree(phdr4note);
 	kfree(elf);
 	kfree(prstatus);
 	kfree(psinfo);
-- 
1.6.5.1


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