Patch "coredump: Ensure proper size of sparse core files" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

coredump: Ensure proper size of sparse core files

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
coredump-ensure-proper-size-of-sparse-core-files.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Dave Kleikamp <[email protected]>
Date: Wed, 11 Jan 2017 13:25:00 -0600
Subject: coredump: Ensure proper size of sparse core files

From: Dave Kleikamp <[email protected]>

[ Upstream commit 4d22c75d4c7b5c5f4bd31054f09103ee490878fd ]

If the last section of a core file ends with an unmapped or zero page, the size of the file does not correspond with the last dump_skip() call. gdb complains that the file is truncated and can be confusing to users.

After all of the vma sections are written, make sure that the file size is no smaller than the current file position.

This problem can be demonstrated with gdb's bigcore testcase on the sparc architecture.

---
 fs/binfmt_elf.c          |    1 +
 fs/coredump.c            |   18 ++++++++++++++++++
 include/linux/coredump.h |    1 +
 3 files changed, 20 insertions(+)

@@ -2295,6 +2295,7 @@ static int elf_core_dump(struct coredump
 				goto end_coredump;
 		}
 	}
+	dump_truncate(cprm);
 
 	if (!elf_core_write_extra_data(cprm))
 		goto end_coredump;

@@ -810,3 +810,21 @@ int dump_align(struct coredump_params *c
 	return mod ? dump_skip(cprm, align - mod) : 1;
 }
 EXPORT_SYMBOL(dump_align);
+
+/*
+ * Ensures that file size is big enough to contain the current file
+ * postion. This prevents gdb from complaining about a truncated file
+ * if the last "write" to the file was dump_skip.
+ */
+void dump_truncate(struct coredump_params *cprm)
+{
+	struct file *file = cprm->file;
+	loff_t offset;
+
+	if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
+		offset = file->f_op->llseek(file, 0, SEEK_CUR);
+		if (i_size_read(file->f_mapping->host) < offset)
+			do_truncate(file->f_path.dentry, offset, 0, file);
+	}
+}
+EXPORT_SYMBOL(dump_truncate);

@@ -14,6 +14,7 @@ struct coredump_params;
 extern int dump_skip(struct coredump_params *cprm, size_t nr);
 extern int dump_emit(struct coredump_params *cprm, const void *addr, int nr);
 extern int dump_align(struct coredump_params *cprm, int align);
+extern void dump_truncate(struct coredump_params *cprm);
 #ifdef CONFIG_COREDUMP
 extern void do_coredump(const siginfo_t *siginfo);
 #else

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/coredump-ensure-proper-size-of-sparse-core-files.patch