2022-07-08 10:21:52

by Jonathan McDowell

Subject: [RFC PATCH 5/7] lib/cpio: Add a parse-only option that doesn't extract any files

In order to allow a CPIO archive to be parsed without actually
extracting anything add a parse_only flag.

Signed-off-by: Jonathan McDowell <[email protected]>
---
include/linux/cpio.h | 2 ++
lib/cpio.c | 35 ++++++++++++++++++++++++++++-------
2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/include/linux/cpio.h b/include/linux/cpio.h
index b05140a565cb..86a43270d186 100644
--- a/include/linux/cpio.h
+++ b/include/linux/cpio.h
@@ -77,6 +77,8 @@ struct cpio_context {
struct cpio_link_hash *link_hash[CPIO_LINK_HASH_SIZE];

struct list_head dir_list;
+
+ bool parse_only;
};

int __cpio cpio_start(struct cpio_context *ctx);
diff --git a/lib/cpio.c b/lib/cpio.c
index 16629ad1e339..36357806eb70 100644
--- a/lib/cpio.c
+++ b/lib/cpio.c
@@ -15,7 +15,12 @@ static ssize_t __cpio xwrite(struct cpio_context *ctx, struct file *file,

/* sys_write only can write MAX_RW_COUNT aka 2G-4K bytes at most */
while (count) {
- ssize_t rv = kernel_write(file, p, count, pos);
+ ssize_t rv;
+
+ if (ctx->parse_only)
+ rv = count;
+ else
+ rv = kernel_write(file, p, count, pos);

if (rv < 0) {
if (rv == -EINTR || rv == -EAGAIN)
@@ -136,7 +141,8 @@ static void __cpio dir_utime(struct cpio_context *ctx)

list_for_each_entry_safe(de, tmp, &ctx->dir_list, list) {
list_del(&de->list);
- do_utime(de->name, de->mtime);
+ if (!ctx->parse_only)
+ do_utime(de->name, de->mtime);
kfree(de);
}
}
@@ -374,6 +380,13 @@ static int __cpio do_name(struct cpio_context *ctx)
free_hash(ctx);
return 0;
}
+
+ if (ctx->parse_only) {
+ if (S_ISREG(ctx->mode))
+ ctx->state = CPIO_COPYFILE;
+ return 0;
+ }
+
clean_path(ctx->collected, ctx->mode);
if (S_ISREG(ctx->mode)) {
int ml = maybe_link(ctx);
@@ -452,8 +465,10 @@ static int __cpio do_copy(struct cpio_context *ctx)
if (ret != ctx->body_len)
return (ret < 0) ? ret : -EIO;

- do_utime_path(&ctx->wfile->f_path, ctx->mtime);
- fput(ctx->wfile);
+ if (!ctx->parse_only) {
+ do_utime_path(&ctx->wfile->f_path, ctx->mtime);
+ fput(ctx->wfile);
+ }
if (ctx->csum_present && ctx->io_csum != ctx->hdr_csum)
return -EBADMSG;

@@ -478,6 +493,12 @@ static int __cpio do_symlink(struct cpio_context *ctx)
struct path path;
int error;

+ ctx->state = CPIO_SKIPIT;
+ ctx->next_state = CPIO_RESET;
+
+ if (ctx->parse_only)
+ return 0;
+
ctx->collected[N_ALIGN(ctx->name_len) + ctx->body_len] = '\0';
clean_path(ctx->collected, 0);

@@ -496,8 +517,7 @@ static int __cpio do_symlink(struct cpio_context *ctx)

cpio_chown(ctx->collected, ctx->uid, ctx->gid, AT_SYMLINK_NOFOLLOW);
do_utime(ctx->collected, ctx->mtime);
- ctx->state = CPIO_SKIPIT;
- ctx->next_state = CPIO_RESET;
+
return 0;
}

@@ -579,7 +599,8 @@ int __cpio cpio_start(struct cpio_context *ctx)

void __cpio cpio_finish(struct cpio_context *ctx)
{
- dir_utime(ctx);
+ if (!ctx->parse_only)
+ dir_utime(ctx);
kfree(ctx->name_buf);
kfree(ctx->symlink_buf);
kfree(ctx->header_buf);
--
2.36.1