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authorDaniel Borkmann <daniel@iogearbox.net>2020-05-15 12:11:18 +0200
committerAlexei Starovoitov <ast@kernel.org>2020-05-15 08:10:36 -0700
commitb2a5212fb634561bb734c6356904e37f6665b955 (patch)
treebb520b4c58247f567a586756c98ab5840d21f8f8 /lib/vsprintf.c
parent47cc0ed574abcbbde0cf143ddb21a0baed1aa2df (diff)
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bpf: Restrict bpf_trace_printk()'s %s usage and add %pks, %pus specifier
Usage of plain %s conversion specifier in bpf_trace_printk() suffers from the very same issue as bpf_probe_read{,str}() helpers, that is, it is broken on archs with overlapping address ranges. While the helpers have been addressed through work in 6ae08ae3dea2 ("bpf: Add probe_read_{user, kernel} and probe_read_{user, kernel}_str helpers"), we need an option for bpf_trace_printk() as well to fix it. Similarly as with the helpers, force users to make an explicit choice by adding %pks and %pus specifier to bpf_trace_printk() which will then pick the corresponding strncpy_from_unsafe*() variant to perform the access under KERNEL_DS or USER_DS. The %pk* (kernel specifier) and %pu* (user specifier) can later also be extended for other objects aside strings that are probed and printed under tracing, and reused out of other facilities like bpf_seq_printf() or BTF based type printing. Existing behavior of %s for current users is still kept working for archs where it is not broken and therefore gated through CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE. For archs not having this property we fall-back to pick probing under KERNEL_DS as a sensible default. Fixes: 8d3b7dce8622 ("bpf: add support for %s specifier to bpf_trace_printk()") Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Reported-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Brendan Gregg <brendan.d.gregg@gmail.com> Link: https://lore.kernel.org/bpf/20200515101118.6508-4-daniel@iogearbox.net
Diffstat (limited to 'lib/vsprintf.c')
-rw-r--r--lib/vsprintf.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 7c488a1ce318..532b6606a18a 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2168,6 +2168,10 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
* f full name
* P node name, including a possible unit address
* - 'x' For printing the address. Equivalent to "%lx".
+ * - '[ku]s' For a BPF/tracing related format specifier, e.g. used out of
+ * bpf_trace_printk() where [ku] prefix specifies either kernel (k)
+ * or user (u) memory to probe, and:
+ * s a string, equivalent to "%s" on direct vsnprintf() use
*
* ** When making changes please also update:
* Documentation/core-api/printk-formats.rst
@@ -2251,6 +2255,14 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
if (!IS_ERR(ptr))
break;
return err_ptr(buf, end, ptr, spec);
+ case 'u':
+ case 'k':
+ switch (fmt[1]) {
+ case 's':
+ return string(buf, end, ptr, spec);
+ default:
+ return error_string(buf, end, "(einval)", spec);
+ }
}
/* default is to _not_ leak addresses, hash before printing */