[DTrace-devel] [PATCH] Improve error checking and reporting for BPF map creation

[Kris Van Hees]

Eugene Loh found that when BPF creation fails due to too big a map,
E2BIG is returned.  This got reported as "Argument list too long"
(using strerror()).  That is not very helpful.  It will now report
"Too big".

In addition, the key and value sizes are size_t entities in the main
caller (dt_bpf_gmap_create()), while create_map() accepts ints for
these values.  And the maximum number of map entries is an int in
dt_bpf_gmap_create() but is at times calculated based on size_t values.
And the bpf(BPF_MAP_CREATE) syscall expects uint32_t values for all
three.  That is now cleaned up.

The debug output in create_gmap() also got a small modification to no
longer report sizes in the success report since it is already reported
at the beginning of the function.

Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
 libdtrace/dt_bpf.c | 31 ++++++++++++++++++++-----------
 1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/libdtrace/dt_bpf.c b/libdtrace/dt_bpf.c
index 5ff348ca..0c97ca7b 100644
--- a/libdtrace/dt_bpf.c
+++ b/libdtrace/dt_bpf.c
@@ -100,8 +100,8 @@ int dt_bpf_prog_load(enum bpf_prog_type prog_type, const dtrace_difo_t *dp,
  * Create a named BPF map.
  */
 int dt_bpf_map_create(enum bpf_map_type map_type, const char *name,
-		      int key_size, int value_size, int max_entries,
-		      uint32_t map_flags)
+		      uint32_t key_size, uint32_t value_size,
+		      uint32_t max_entries, uint32_t map_flags)
 {
 	union bpf_attr	attr;
 
@@ -242,26 +242,35 @@ dt_bpf_init_helpers(dtrace_hdl_t *dtp)
 
 static int
 create_gmap(dtrace_hdl_t *dtp, const char *name, enum bpf_map_type type,
-	    int ksz, int vsz, int size)
+	    size_t ksz, size_t vsz, size_t size)
 {
-	int		fd;
+	int		fd, err;
 	dt_ident_t	*idp;
 
-	dt_dprintf("Creating BPF map '%s' (ksz %u, vsz %u, sz %d)\n",
+	dt_dprintf("Creating BPF map '%s' (ksz %lu, vsz %lu, sz %lu)\n",
 		   name, ksz, vsz, size);
-	fd = dt_bpf_map_create(type, name, ksz, vsz, size, 0);
+
+	if (ksz > UINT_MAX || vsz > UINT_MAX || size > UINT_MAX) {
+		fd = -1;
+		err = E2BIG;
+	} else {
+		fd = dt_bpf_map_create(type, name, ksz, vsz, size, 0);
+		err = errno;
+	}
+
 	if (fd < 0) {
 		char msg[64];
 
 		snprintf(msg, sizeof(msg),
 			 "failed to create BPF map '%s'", name);
-		if (errno == EPERM)
+		if (err == E2BIG)
+			return dt_bpf_error(dtp, "%s: Too big\n", msg);
+		if (err == EPERM)
 			return dt_bpf_lockmem_error(dtp, msg);
-		return dt_bpf_error(dtp, "%s: %s\n", msg, strerror(errno));
+		return dt_bpf_error(dtp, "%s: %s\n", msg, strerror(err));
 	}
 
-	dt_dprintf("BPF map '%s' is FD %d (ksz %u, vsz %u, sz %d)\n",
-		   name, fd, ksz, vsz, size);
+	dt_dprintf("BPF map '%s' is FD %d\n", name, fd);
 
 	/*
 	 * Assign the fd as id for the BPF map identifier.
@@ -354,7 +363,7 @@ populate_probes_map(dtrace_hdl_t *dtp, int fd)
 int
 dt_bpf_gmap_create(dtrace_hdl_t *dtp)
 {
-	int		sz;
+	size_t		sz;
 	int		dvarc = 0;
 	int		ci_mapfd, st_mapfd, pr_mapfd;
 	uint64_t	key = 0;
-- 
2.34.1