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Optimize save_path_to_str_buf in tracee.bpf.c #758

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Jun 9, 2021
Merged

Optimize save_path_to_str_buf in tracee.bpf.c #758

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35 changes: 22 additions & 13 deletions tracee-ebpf/tracee/tracee.bpf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1172,38 +1172,47 @@ static __always_inline int save_path_to_str_buf(buf_t *string_p, const struct pa
int zero = 0;
struct dentry *dentry = f_path.dentry;
struct vfsmount *vfsmnt = f_path.mnt;
struct mount *mnt_parent_p;

struct mount *mnt_p = real_mount(vfsmnt);
struct mount mnt;
bpf_probe_read(&mnt, sizeof(struct mount), mnt_p);
bpf_probe_read(&mnt_parent_p, sizeof(struct mount*), &mnt_p->mnt_parent);

u32 buf_off = (MAX_PERCPU_BUFSIZE >> 1);
struct dentry *mnt_root;
struct dentry *d_parent;
struct qstr d_name;
unsigned int len;
unsigned int off;
int sz;

#pragma unroll
// As bpf loops are not allowed and max instructions number is 4096, path components is limited to 30
for (int i = 0; i < 30; i++) {
struct dentry *mnt_root = get_mnt_root_ptr_from_vfsmnt(vfsmnt);
struct dentry *d_parent = get_d_parent_ptr_from_dentry(dentry);
mnt_root = get_mnt_root_ptr_from_vfsmnt(vfsmnt);
d_parent = get_d_parent_ptr_from_dentry(dentry);
if (dentry == mnt_root || dentry == d_parent) {
if (dentry != mnt_root) {
// We reached root, but not mount root - escaped?
break;
}
if (mnt_p != mnt.mnt_parent) {
if (mnt_p != mnt_parent_p) {
// We reached root, but not global root - continue with mount point path
dentry = mnt.mnt_mountpoint;
bpf_probe_read(&mnt, sizeof(struct mount), mnt.mnt_parent);
vfsmnt = &mnt.mnt;
bpf_probe_read(&dentry, sizeof(struct dentry*), &mnt_p->mnt_mountpoint);
bpf_probe_read(&mnt_p, sizeof(struct mount*), &mnt_p->mnt_parent);
bpf_probe_read(&mnt_parent_p, sizeof(struct mount*), &mnt_p->mnt_parent);
bpf_probe_read(&vfsmnt, sizeof(struct vfsmount*), (const void*)&mnt_p->mnt);
continue;
}
// Global root - path fully parsed
break;
}
// Add this dentry name to path
struct qstr d_name = get_d_name_from_dentry(dentry);
unsigned int len = (d_name.len+1) & (MAX_STRING_SIZE-1);
unsigned int off = buf_off - len;
d_name = get_d_name_from_dentry(dentry);
len = (d_name.len+1) & (MAX_STRING_SIZE-1);
off = buf_off - len;

// Is string buffer big enough for dentry name?
int sz = 0;
sz = 0;
if (off <= buf_off) { // verify no wrap occured
len = len & ((MAX_PERCPU_BUFSIZE >> 1)-1);
sz = bpf_probe_read_str(&(string_p->buf[off & ((MAX_PERCPU_BUFSIZE >> 1)-1)]), len, (void *)d_name.name);
Expand All @@ -1224,7 +1233,7 @@ static __always_inline int save_path_to_str_buf(buf_t *string_p, const struct pa
if (buf_off == (MAX_PERCPU_BUFSIZE >> 1)) {
// memfd files have no path in the filesystem -> extract their name
buf_off = 0;
struct qstr d_name = get_d_name_from_dentry(dentry);
d_name = get_d_name_from_dentry(dentry);
bpf_probe_read_str(&(string_p->buf[0]), MAX_STRING_SIZE, (void *)d_name.name);
} else {
// Add leading slash
Expand Down